Toolbar: No ActivityTabProvider in toolbar/

This CL removes the dependency on ActivityTab{Provider/TabObserver} in
toolbar/ package. They are replaced with a new CurrentTabObserver that
works as a stop-gap solution.

Bug: 1127732
Change-Id: I69e4272d38e26e70e62c31a6400859832dd70a2f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2505297
Commit-Queue: Jinsuk Kim <jinsukkim@chromium.org>
Reviewed-by: Filip Gorski <fgorski@chromium.org>
Cr-Commit-Position: refs/heads/master@{#826541}

chrome/android/java/src/org/chromium/chrome/browser/tabbed_mode/TabbedRootUiCoordinator.java

@@ -18,6 +18,7 @@ import org.chromium.base.supplier.OneshotSupplier;
 import org.chromium.base.supplier.Supplier;
 import org.chromium.chrome.R;
 import org.chromium.chrome.browser.ActivityTabProvider;
+import org.chromium.chrome.browser.ActivityTabProvider.ActivityTabTabObserver;
 import org.chromium.chrome.browser.app.ChromeActivity;
 import org.chromium.chrome.browser.app.appmenu.AppMenuPropertiesDelegateImpl;
 import org.chromium.chrome.browser.banners.AppBannerInProductHelpController;
@@ -87,6 +88,8 @@ public class TabbedRootUiCoordinator extends RootUiCoordinator {
     private NavigationSheet mNavigationSheet;
     private ComposedBrowserControlsVisibilityDelegate mAppBrowserControlsVisibilityDelegate;
     private LayoutManagerImpl mLayoutManager;
+    private ObservableSupplierImpl<Tab> mToolbarButtonIphTabSupplier;
+    private ActivityTabTabObserver mToolbarButtonIphTabObserver;
 
     /**
      * Construct a new TabbedRootUiCoordinator.
@@ -155,6 +158,7 @@ public class TabbedRootUiCoordinator extends RootUiCoordinator {
 
         if (mToolbarButtonInProductHelpController != null) {
             mToolbarButtonInProductHelpController.destroy();
+            mToolbarButtonIphTabObserver.destroy();
         }
 
         if (mAppBannerInProductHelpController != null) {
@@ -309,9 +313,19 @@ public class TabbedRootUiCoordinator extends RootUiCoordinator {
 
     private void initializeIPH(boolean intentWithEffect) {
         if (mActivity == null) return;
+        mToolbarButtonIphTabSupplier = new ObservableSupplierImpl<>();
         mToolbarButtonInProductHelpController =
                 new ToolbarButtonInProductHelpController(mActivity, mAppMenuCoordinator,
-                        mActivity.getLifecycleDispatcher(), mActivity.getActivityTabProvider());
+                        mActivity.getLifecycleDispatcher(), mToolbarButtonIphTabSupplier);
+        ActivityTabProvider activityTabProvider = mActivity.getActivityTabProvider();
+        mToolbarButtonIphTabObserver = new ActivityTabTabObserver(activityTabProvider) {
+            @Override
+            public void onObservingDifferentTab(Tab tab, boolean hint) {
+                mToolbarButtonIphTabSupplier.set(tab);
+            }
+        };
+        mToolbarButtonIphTabSupplier.set(activityTabProvider.get());
+
         boolean didTriggerPromo = triggerPromo(intentWithEffect);
         if (!didTriggerPromo) {
             mToolbarButtonInProductHelpController.showColdStartIPH();

chrome/android/java/src/org/chromium/chrome/browser/toolbar/ToolbarButtonInProductHelpController.java

@@ -5,10 +5,11 @@ package org.chromium.chrome.browser.toolbar;
 
 import android.os.Handler;
 
+import androidx.annotation.NonNull;
+
+import org.chromium.base.supplier.ObservableSupplier;
 import org.chromium.base.task.PostTask;
 import org.chromium.chrome.R;
-import org.chromium.chrome.browser.ActivityTabProvider;
-import org.chromium.chrome.browser.ActivityTabProvider.ActivityTabTabObserver;
 import org.chromium.chrome.browser.ChromeTabbedActivity;
 import org.chromium.chrome.browser.app.ChromeActivity;
 import org.chromium.chrome.browser.app.appmenu.AppMenuPropertiesDelegateImpl;
@@ -24,6 +25,8 @@ import org.chromium.chrome.browser.net.spdyproxy.DataReductionProxySettings;
 import org.chromium.chrome.browser.offlinepages.OfflinePageBridge;
 import org.chromium.chrome.browser.previews.Previews;
 import org.chromium.chrome.browser.profiles.Profile;
+import org.chromium.chrome.browser.tab.CurrentTabObserver;
+import org.chromium.chrome.browser.tab.EmptyTabObserver;
 import org.chromium.chrome.browser.tab.Tab;
 import org.chromium.chrome.browser.translate.TranslateBridge;
 import org.chromium.chrome.browser.translate.TranslateUtils;
@@ -46,7 +49,7 @@ import org.chromium.content_public.browser.UiThreadTaskTraits;
  */
 public class ToolbarButtonInProductHelpController
         implements ScreenshotMonitorDelegate, PauseResumeWithNativeObserver {
-    private final ActivityTabTabObserver mPageLoadObserver;
+    private final CurrentTabObserver mPageLoadObserver;
     private final ChromeActivity mActivity;
     private final AppMenuPropertiesDelegate mAppMenuPropertiesDelegate;
     private final ScreenshotMonitor mScreenshotMonitor;
@@ -54,15 +57,23 @@ public class ToolbarButtonInProductHelpController
     private UserEducationHelper mUserEducationHelper;
     private final Handler mHandler = new Handler();
 
-    public ToolbarButtonInProductHelpController(final ChromeActivity activity,
-            AppMenuCoordinator appMenuCoordinator, ActivityLifecycleDispatcher lifecycleDispatcher,
-            ActivityTabProvider tabProvider) {
+    /**
+     * @param activity {@link ChromeActivity} on which this class runs.
+     * @param appMenuCoordinator {@link AppMenuCoordinator} whose visual state is to be updated
+     *        accordingly.
+     * @param lifecycleDispatcher {@link LifecycleDispatcher} that helps observe activity lifecycle.
+     * @param tabSupplier An observable supplier of the current {@link Tab}.
+     */
+    public ToolbarButtonInProductHelpController(@NonNull final ChromeActivity activity,
+            @NonNull AppMenuCoordinator appMenuCoordinator,
+            @NonNull ActivityLifecycleDispatcher lifecycleDispatcher,
+            @NonNull ObservableSupplier<Tab> tabSupplier) {
         mActivity = activity;
         mUserEducationHelper =
                 new UserEducationHelper(mActivity, mHandler, TrackerFactory::getTrackerForProfile);
         mScreenshotMonitor = new ScreenshotMonitor(this);
         lifecycleDispatcher.register(this);
-        mPageLoadObserver = new ActivityTabTabObserver(tabProvider) {
+        mPageLoadObserver = new CurrentTabObserver(tabSupplier, new EmptyTabObserver() {
             /**
              * Stores total data saved at the start of a page load. Used to calculate delta at the
              * end of page load, which is just an estimate of the data saved for the current page
@@ -125,16 +136,14 @@ public class ToolbarButtonInProductHelpController
                         Profile.fromWebContents(tab.getWebContents()));
                 tracker.notifyEvent(EventConstants.USER_HAS_SEEN_DINO);
             }
-        };
+        });
 
         mAppMenuHandler = appMenuCoordinator.getAppMenuHandler();
         mAppMenuPropertiesDelegate = appMenuCoordinator.getAppMenuPropertiesDelegate();
     }
 
     public void destroy() {
-        if (mPageLoadObserver != null) {
-            mPageLoadObserver.destroy();
-        }
+        mPageLoadObserver.destroy();
     }
 
     /**

chrome/android/java/src/org/chromium/chrome/browser/toolbar/ToolbarManager.java

@@ -46,7 +46,9 @@ import org.chromium.chrome.browser.compositor.Invalidator;
 import org.chromium.chrome.browser.compositor.layouts.Layout;
 import org.chromium.chrome.browser.compositor.layouts.LayoutManagerImpl;
 import org.chromium.chrome.browser.compositor.layouts.SceneChangeObserver;
+import org.chromium.chrome.browser.compositor.overlays.toolbar.TopToolbarOverlayCoordinator;
 import org.chromium.chrome.browser.customtabs.features.toolbar.CustomTabToolbar;
+import org.chromium.chrome.browser.device.DeviceClassManager;
 import org.chromium.chrome.browser.feature_engagement.TrackerFactory;
 import org.chromium.chrome.browser.findinpage.FindToolbarManager;
 import org.chromium.chrome.browser.findinpage.FindToolbarObserver;
@@ -160,6 +162,8 @@ public class ToolbarManager implements UrlFocusChangeListener, ThemeColorObserve
 
     private ObservableSupplierImpl<BottomControlsCoordinator> mBottomControlsCoordinatorSupplier =
             new ObservableSupplierImpl<>();
+    private final ObservableSupplierImpl<Tab> mActivityTabSupplier = new ObservableSupplierImpl<>();
+    private TopToolbarOverlayCoordinator mOverlayCoordinator;
     private TabModelSelector mTabModelSelector;
     private TabModelSelectorObserver mTabModelSelectorObserver;
     private ObservableSupplier<TabModelSelector> mTabModelSelectorSupplier;
@@ -436,14 +440,15 @@ public class ToolbarManager implements UrlFocusChangeListener, ThemeColorObserve
         }
 
         mProgressBarCoordinator =
-                new LoadProgressCoordinator(mActivityTabProvider, mToolbar.getProgressBar());
-
+                new LoadProgressCoordinator(mActivityTabSupplier, mToolbar.getProgressBar());
         mToolbar.addUrlExpansionObserver(statusBarColorController);
 
         mActivityTabTabObserver = new ActivityTabProvider.ActivityTabTabObserver(
                 mActivityTabProvider) {
             @Override
             public void onObservingDifferentTab(Tab tab, boolean hint) {
+                mActivityTabSupplier.set(tab);
+
                 // ActivityTabProvider will null out the tab passed to onObservingDifferentTab when
                 // the tab is non-interactive (e.g. when entering the TabSwitcher), but in those
                 // cases we actually still want to use the most recently selected tab.
@@ -927,9 +932,10 @@ public class ToolbarManager implements UrlFocusChangeListener, ThemeColorObserve
         // clang-format off
         mBottomControlsCoordinatorSupplier.set(new BottomControlsCoordinator(mBrowserControlsSizer,
                 mFullscreenManager, mActivity.findViewById(R.id.bottom_controls_stub),
-                mActivityTabProvider, mAppThemeColorProvider, mShareDelegateSupplier,
+                mAppThemeColorProvider, mShareDelegateSupplier,
                 mMenuButtonCoordinator.getMenuButtonHelperSupplier(),
-                mToolbarTabController::openHomepage, (reason) -> setUrlBarFocus(true, reason),
+                mToolbarTabController::openHomepage,
+                mCallbackController.makeCancelable((reason) -> setUrlBarFocus(true, reason)),
                 mScrimCoordinator, mOmniboxFocusStateSupplier));
         // clang-format on
     }
@@ -972,8 +978,18 @@ public class ToolbarManager implements UrlFocusChangeListener, ThemeColorObserve
 
         mToolbar.initializeWithNative(layoutManager::requestUpdate, tabSwitcherClickHandler,
                 tabSwitcherLongClickHandler, newTabClickHandler, bookmarkClickHandler,
-                customTabsBackClickHandler, layoutManager, mActivityTabProvider,
-                mBrowserControlsSizer);
+                customTabsBackClickHandler, mBrowserControlsSizer);
+        // If fullscreen is disabled, don't bother creating this overlay; only the android view will
+        // ever be shown.
+        if (DeviceClassManager.enableFullscreen()) {
+            mOverlayCoordinator = new TopToolbarOverlayCoordinator(mActivity, layoutManager,
+                    mControlContainer::getProgressBarDrawingInfo, mActivityTabProvider,
+                    mBrowserControlsSizer, layoutManager::getResourceManager);
+            layoutManager.addSceneOverlay(mOverlayCoordinator);
+            ToolbarLayout toolbarLayout = mActivity.findViewById(R.id.toolbar);
+            toolbarLayout.setOverlayVisibilityCallback(mCallbackController.makeCancelable(
+                    mOverlayCoordinator::setIsAndroidViewVisible));
+        }
 
         mToolbar.addOnAttachStateChangeListener(new OnAttachStateChangeListener() {
             @Override
@@ -1038,18 +1054,18 @@ public class ToolbarManager implements UrlFocusChangeListener, ThemeColorObserve
                     mActivity, mHandler, TrackerFactory::getTrackerForProfile);
             View homeButton = mControlContainer.findViewById(R.id.home_button);
             mHomeButtonCoordinator = new HomeButtonCoordinator(mActivity, homeButton,
-                    mActivityTabProvider, userEducationHelper,
-                    mIncognitoStateProvider::isIncognitoSelected, mIntentMetadataOneshotSupplier,
-                    mPromoShownOneshotSupplier, HomepageManager::isHomepageNonNtp);
+                    userEducationHelper, mIncognitoStateProvider::isIncognitoSelected,
+                    mIntentMetadataOneshotSupplier, mPromoShownOneshotSupplier,
+                    HomepageManager::isHomepageNonNtp, mActivityTabSupplier);
             ToggleTabStackButton toggleTabStackButton =
                     mControlContainer.findViewById(R.id.tab_switcher_button);
             mToggleTabStackButtonCoordinator = new ToggleTabStackButtonCoordinator(mActivity,
-                    toggleTabStackButton, mActivityTabProvider, userEducationHelper,
+                    toggleTabStackButton, userEducationHelper,
                     mIncognitoStateProvider::isIncognitoSelected, mIntentMetadataOneshotSupplier,
                     mPromoShownOneshotSupplier, mLayoutStateProviderSupplier,
-                    mToolbar::setNewTabButtonHighlight);
+                    mToolbar::setNewTabButtonHighlight, mActivityTabSupplier);
         }
-
+        mActivityTabSupplier.set(mActivityTabProvider.get());
         TraceEvent.end("ToolbarManager.initializeWithNative");
     }
 
@@ -1144,6 +1160,11 @@ public class ToolbarManager implements UrlFocusChangeListener, ThemeColorObserve
             mBottomControlsCoordinatorSupplier = null;
         }
 
+        if (mOverlayCoordinator != null) {
+            mOverlayCoordinator.destroy();
+            mOverlayCoordinator = null;
+        }
+
         mToolbar.removeUrlExpansionObserver(mStatusBarColorController);
         mToolbar.destroy();
 
@@ -1173,6 +1194,8 @@ public class ToolbarManager implements UrlFocusChangeListener, ThemeColorObserve
             mActivityTabTabObserver = null;
         }
 
+        if (mProgressBarCoordinator != null) mProgressBarCoordinator.destroy();
+
         if (mFindToolbarManager != null) {
             mFindToolbarManager.removeObserver(mFindToolbarObserver);
             mFindToolbarManager = null;

chrome/android/java/src/org/chromium/chrome/browser/toolbar/bottom/BottomControlsCoordinator.java

@@ -17,7 +17,6 @@ import org.chromium.base.Callback;
 import org.chromium.base.supplier.ObservableSupplier;
 import org.chromium.base.supplier.Supplier;
 import org.chromium.chrome.R;
-import org.chromium.chrome.browser.ActivityTabProvider;
 import org.chromium.chrome.browser.browser_controls.BrowserControlsSizer;
 import org.chromium.chrome.browser.compositor.layouts.LayoutManagerImpl;
 import org.chromium.chrome.browser.fullscreen.FullscreenManager;
@@ -64,7 +63,6 @@ public class BottomControlsCoordinator {
      *                          height for the renderer.
      * @param fullscreenManager A {@link FullscreenManager} to listen for fullscreen changes.
      * @param stub The bottom controls {@link ViewStub} to inflate.
-     * @param tabProvider
      * @param themeColorProvider The {@link ThemeColorProvider} for the bottom toolbar.
      * @param shareDelegateSupplier The supplier for the {@link ShareDelegate} the bottom controls
      *         should use to share content.
@@ -76,7 +74,7 @@ public class BottomControlsCoordinator {
      */
     @SuppressLint("CutPasteId") // Not actually cut and paste since it's View vs ViewGroup.
     public BottomControlsCoordinator(BrowserControlsSizer controlsSizer,
-            FullscreenManager fullscreenManager, ViewStub stub, ActivityTabProvider tabProvider,
+            FullscreenManager fullscreenManager, ViewStub stub,
             ThemeColorProvider themeColorProvider,
             ObservableSupplier<ShareDelegate> shareDelegateSupplier,
             ObservableSupplier<AppMenuButtonHelper> menuButtonHelperSupplier,

chrome/android/java/src/org/chromium/chrome/browser/toolbar/load_progress/LoadProgressCoordinator.java

@@ -4,7 +4,10 @@
 
 package org.chromium.chrome.browser.toolbar.load_progress;
 
-import org.chromium.chrome.browser.ActivityTabProvider;
+import androidx.annotation.NonNull;
+
+import org.chromium.base.supplier.ObservableSupplier;
+import org.chromium.chrome.browser.tab.Tab;
 import org.chromium.chrome.browser.toolbar.ToolbarProgressBar;
 import org.chromium.ui.modelutil.PropertyKey;
 import org.chromium.ui.modelutil.PropertyModel;
@@ -21,11 +24,15 @@ public class LoadProgressCoordinator {
     private final PropertyModelChangeProcessor<PropertyModel, ToolbarProgressBar, PropertyKey>
             mPropertyModelChangeProcessor;
 
-    public LoadProgressCoordinator(
-            ActivityTabProvider activityTabProvider, ToolbarProgressBar progressBarView) {
+    /**
+     * @param tabSupplier An observable supplier of the current {@link Tab}.
+     * @param progressBarView Toolbar progress bar view.
+     */
+    public LoadProgressCoordinator(@NonNull ObservableSupplier<Tab> tabSupplier,
+            @NonNull ToolbarProgressBar progressBarView) {
         mProgressBarView = progressBarView;
         mModel = new PropertyModel(LoadProgressProperties.ALL_KEYS);
-        mMediator = new LoadProgressMediator(activityTabProvider, mModel);
+        mMediator = new LoadProgressMediator(tabSupplier, mModel);
         mLoadProgressViewBinder = new LoadProgressViewBinder();
 
         mPropertyModelChangeProcessor = PropertyModelChangeProcessor.create(
@@ -47,4 +54,9 @@ public class LoadProgressCoordinator {
     public void setPreventUpdates(boolean preventUpdates) {
         mMediator.setPreventUpdates(preventUpdates);
     }
+
+    /** Destroy load progress bar object. */
+    public void destroy() {
+        mMediator.destroy();
+    }
 }

chrome/android/java/src/org/chromium/chrome/browser/toolbar/load_progress/LoadProgressMediator.java

@@ -4,8 +4,11 @@
 
 package org.chromium.chrome.browser.toolbar.load_progress;
 
+import androidx.annotation.NonNull;
+
 import org.chromium.base.MathUtils;
-import org.chromium.chrome.browser.ActivityTabProvider;
+import org.chromium.base.supplier.ObservableSupplier;
+import org.chromium.chrome.browser.tab.CurrentTabObserver;
 import org.chromium.chrome.browser.tab.EmptyTabObserver;
 import org.chromium.chrome.browser.tab.Tab;
 import org.chromium.chrome.browser.toolbar.load_progress.LoadProgressProperties.CompletionState;
@@ -23,15 +26,20 @@ public class LoadProgressMediator {
     static final float MINIMUM_LOAD_PROGRESS = 0.05f;
 
     private final PropertyModel mModel;
-    private final EmptyTabObserver mTabObserver;
+    private final CurrentTabObserver mTabObserver;
     private final LoadProgressSimulator mLoadProgressSimulator;
     private boolean mPreventUpdates;
 
-    public LoadProgressMediator(ActivityTabProvider activityTabProvider, PropertyModel model) {
+    /**
+     * @param tabSupplier An observable supplier of the current {@link Tab}.
+     * @param model MVC property model instance used for load progress bar.
+     */
+    public LoadProgressMediator(
+            @NonNull ObservableSupplier<Tab> tabSupplier, @NonNull PropertyModel model) {
         mModel = model;
         mLoadProgressSimulator = new LoadProgressSimulator(model);
 
-        mTabObserver = new ActivityTabProvider.ActivityTabTabObserver(activityTabProvider) {
+        mTabObserver = new CurrentTabObserver(tabSupplier, new EmptyTabObserver() {
             @Override
             public void onDidStartNavigation(Tab tab, NavigationHandle navigation) {
                 if (navigation.isSameDocument() || !navigation.isInMainFrame()) {
@@ -84,13 +92,10 @@ public class LoadProgressMediator {
             public void onCrash(Tab tab) {
                 finishLoadProgress(false);
             }
+        });
 
-            @Override
-            protected void onObservingDifferentTab(Tab tab, boolean hint) {
-                onNewTabObserved(tab);
-            }
-        };
-        onNewTabObserved(activityTabProvider.get());
+        tabSupplier.addObserver(this::onNewTabObserved);
+        onNewTabObserved(tabSupplier.get());
     }
 
     /**
@@ -152,4 +157,9 @@ public class LoadProgressMediator {
                                                 : CompletionState.FINISHED_DONT_ANIMATE;
         mModel.set(LoadProgressProperties.COMPLETION_STATE, completionState);
     }
+
+    /** Destroy load progress bar object. */
+    public void destroy() {
+        mTabObserver.destroy();
+    }
 }

chrome/android/java/src/org/chromium/chrome/browser/toolbar/top/HomeButtonCoordinator.java

@@ -7,16 +7,20 @@ package org.chromium.chrome.browser.toolbar.top;
 import android.content.Context;
 import android.view.View;
 
+import androidx.annotation.NonNull;
+import androidx.annotation.Nullable;
 import androidx.annotation.VisibleForTesting;
 
 import org.chromium.base.supplier.BooleanSupplier;
+import org.chromium.base.supplier.ObservableSupplier;
 import org.chromium.base.supplier.OneshotSupplier;
 import org.chromium.base.supplier.Supplier;
 import org.chromium.chrome.R;
-import org.chromium.chrome.browser.ActivityTabProvider;
 import org.chromium.chrome.browser.feed.shared.FeedFeatures;
 import org.chromium.chrome.browser.flags.FeatureParamUtils;
 import org.chromium.chrome.browser.intent.IntentMetadata;
+import org.chromium.chrome.browser.tab.CurrentTabObserver;
+import org.chromium.chrome.browser.tab.EmptyTabObserver;
 import org.chromium.chrome.browser.tab.Tab;
 import org.chromium.chrome.browser.toolbar.HomeButton;
 import org.chromium.chrome.browser.user_education.IPHCommandBuilder;
@@ -40,7 +44,7 @@ public class HomeButtonCoordinator {
     private final View mHomeButton;
     private final UserEducationHelper mUserEducationHelper;
     private final BooleanSupplier mIsIncognitoSupplier;
-    private final ActivityTabProvider.ActivityTabTabObserver mPageLoadObserver;
+    private final CurrentTabObserver mPageLoadObserver;
     private final OneshotSupplier<IntentMetadata> mIntentMetadataOneshotSupplier;
     private final OneshotSupplier<Boolean> mPromoShownOneshotSupplier;
     private final Supplier<Boolean> mIsHomepageNonNtpSupplier;
@@ -48,19 +52,20 @@ public class HomeButtonCoordinator {
     /**
      * @param context The Android context used for various view operations.
      * @param homeButton The concrete {@link View} class for this MVC component.
-     * @param activityTabProvider Provides the current active tab.
      * @param userEducationHelper Helper class for showing in-product help text bubbles.
      * @param isIncognitoSupplier Supplier for whether the current tab is incognito.
      * @param intentMetadataOneshotSupplier Potentially delayed information about launching intent.
      * @param promoShownOneshotSupplier Potentially delayed information about if a promo was shown.
      * @param isHomepageNonNtpSupplier Supplier for whether the current homepage is not NTP.
+     * @param tabSupplier Supplier of the activity tab.
      */
-    public HomeButtonCoordinator(Context context, View homeButton,
-            ActivityTabProvider activityTabProvider, UserEducationHelper userEducationHelper,
-            BooleanSupplier isIncognitoSupplier,
-            OneshotSupplier<IntentMetadata> intentMetadataOneshotSupplier,
-            OneshotSupplier<Boolean> promoShownOneshotSupplier,
-            Supplier<Boolean> isHomepageNonNtpSupplier) {
+    public HomeButtonCoordinator(@NonNull Context context, @Nullable View homeButton,
+            @NonNull UserEducationHelper userEducationHelper,
+            @NonNull BooleanSupplier isIncognitoSupplier,
+            @NonNull OneshotSupplier<IntentMetadata> intentMetadataOneshotSupplier,
+            @NonNull OneshotSupplier<Boolean> promoShownOneshotSupplier,
+            @NonNull Supplier<Boolean> isHomepageNonNtpSupplier,
+            @NonNull ObservableSupplier<Tab> tabSupplier) {
         mContext = context;
         mHomeButton = homeButton;
         mUserEducationHelper = userEducationHelper;
@@ -68,17 +73,16 @@ public class HomeButtonCoordinator {
         mIntentMetadataOneshotSupplier = intentMetadataOneshotSupplier;
         mPromoShownOneshotSupplier = promoShownOneshotSupplier;
         mIsHomepageNonNtpSupplier = isHomepageNonNtpSupplier;
-        mPageLoadObserver = new ActivityTabProvider.ActivityTabTabObserver(activityTabProvider) {
+        mPageLoadObserver = new CurrentTabObserver(tabSupplier, new EmptyTabObserver() {
             @Override
             public void onPageLoadFinished(Tab tab, String url) {
                 handlePageLoadFinished(url);
             }
-        };
+        });
     }
 
     /** Cleans up observers. */
     public void destroy() {
-        // This will unsubscribe the observer.
         mPageLoadObserver.destroy();
     }
 

chrome/android/java/src/org/chromium/chrome/browser/toolbar/top/ToggleTabStackButtonCoordinator.java

@@ -11,13 +11,15 @@ import androidx.annotation.VisibleForTesting;
 import org.chromium.base.Callback;
 import org.chromium.base.CallbackController;
 import org.chromium.base.supplier.BooleanSupplier;
+import org.chromium.base.supplier.ObservableSupplier;
 import org.chromium.base.supplier.OneshotSupplier;
 import org.chromium.chrome.R;
-import org.chromium.chrome.browser.ActivityTabProvider;
 import org.chromium.chrome.browser.flags.FeatureParamUtils;
 import org.chromium.chrome.browser.intent.IntentMetadata;
 import org.chromium.chrome.browser.layouts.LayoutStateProvider;
 import org.chromium.chrome.browser.layouts.LayoutType;
+import org.chromium.chrome.browser.tab.CurrentTabObserver;
+import org.chromium.chrome.browser.tab.EmptyTabObserver;
 import org.chromium.chrome.browser.tab.Tab;
 import org.chromium.chrome.browser.user_education.IPHCommandBuilder;
 import org.chromium.chrome.browser.user_education.UserEducationHelper;
@@ -44,11 +46,10 @@ public class ToggleTabStackButtonCoordinator {
     private final OneshotSupplier<IntentMetadata> mIntentMetadataOneshotSupplier;
     private final OneshotSupplier<Boolean> mPromoShownOneshotSupplier;
     private final Callback<Boolean> mSetNewTabButtonHighlightCallback;
+    private final CurrentTabObserver mPageLoadObserver;
 
     private LayoutStateProvider mLayoutStateProvider;
     private LayoutStateProvider.LayoutStateObserver mLayoutStateObserver;
-
-    private ActivityTabProvider.ActivityTabTabObserver mPageLoadObserver;
     private boolean mIphBeingShown;
 
     /**
@@ -62,15 +63,16 @@ public class ToggleTabStackButtonCoordinator {
      * @param promoShownOneshotSupplier Potentially delayed information about if a promo was shown.
      * @param layoutStateProviderSupplier Allows observing layout state.
      * @param setNewTabButtonHighlightCallback Delegate to highlight the new tab button.
-     *
+     * @param activityTabSupplier Supplier of the activity tab.
      */
     public ToggleTabStackButtonCoordinator(Context context,
-            ToggleTabStackButton toggleTabStackButton, ActivityTabProvider activityTabProvider,
-            UserEducationHelper userEducationHelper, BooleanSupplier isIncognitoSupplier,
+            ToggleTabStackButton toggleTabStackButton, UserEducationHelper userEducationHelper,
+            BooleanSupplier isIncognitoSupplier,
             OneshotSupplier<IntentMetadata> intentMetadataOneshotSupplier,
             OneshotSupplier<Boolean> promoShownOneshotSupplier,
             OneshotSupplier<LayoutStateProvider> layoutStateProviderSupplier,
-            Callback<Boolean> setNewTabButtonHighlightCallback) {
+            Callback<Boolean> setNewTabButtonHighlightCallback,
+            ObservableSupplier<Tab> activityTabSupplier) {
         mContext = context;
         mToggleTabStackButton = toggleTabStackButton;
         mUserEducationHelper = userEducationHelper;
@@ -81,22 +83,19 @@ public class ToggleTabStackButtonCoordinator {
 
         layoutStateProviderSupplier.onAvailable(
                 mCallbackController.makeCancelable(this::setLayoutStateProvider));
-        mPageLoadObserver = new ActivityTabProvider.ActivityTabTabObserver(activityTabProvider) {
+        mPageLoadObserver = new CurrentTabObserver(activityTabSupplier, new EmptyTabObserver() {
             @Override
             public void onPageLoadFinished(Tab tab, String url) {
                 handlePageLoadFinished();
             }
-        };
+        });
     }
 
     /** Cleans up callbacks and observers. */
     public void destroy() {
         mCallbackController.destroy();
 
-        if (mPageLoadObserver != null) {
-            mPageLoadObserver.destroy();
-            mPageLoadObserver = null;
-        }
+        mPageLoadObserver.destroy();
 
         if (mLayoutStateProvider != null) {
             mLayoutStateProvider.removeObserver(mLayoutStateObserver);
@@ -133,7 +132,6 @@ public class ToggleTabStackButtonCoordinator {
         mLayoutStateProvider.addObserver(mLayoutStateObserver);
     }
 
-    // TODO(https://crbug.com/1133355): Reduce visibility once ActivityTabTabObserver is mockable.
     @VisibleForTesting
     void handlePageLoadFinished() {
         if (mToggleTabStackButton == null || !mToggleTabStackButton.isShown()) return;
@@ -175,4 +173,4 @@ public class ToggleTabStackButtonCoordinator {
         mIphBeingShown = false;
         mToggleTabStackButton.setHighlightDrawable(false);
     }
-}
+}
\ No newline at end of file

chrome/android/java/src/org/chromium/chrome/browser/toolbar/top/ToolbarLayout.java

@@ -26,7 +26,6 @@ import org.chromium.base.Callback;
 import org.chromium.base.ObserverList;
 import org.chromium.base.TraceEvent;
 import org.chromium.chrome.R;
-import org.chromium.chrome.browser.compositor.overlays.toolbar.TopToolbarOverlayCoordinator;
 import org.chromium.chrome.browser.findinpage.FindToolbar;
 import org.chromium.chrome.browser.omnibox.LocationBar;
 import org.chromium.chrome.browser.omnibox.LocationBarCoordinator;
@@ -84,7 +83,7 @@ public abstract class ToolbarLayout
     private MenuButtonCoordinator mMenuButtonCoordinator;
     private AppMenuButtonHelper mAppMenuButtonHelper;
 
-    private TopToolbarOverlayCoordinator mOverlayCoordinator;
+    private Callback<Boolean> mOverlayVisibilityCallback;
     private Runnable mTabOrModelChangeRunnable;
 
     /**
@@ -125,17 +124,20 @@ public abstract class ToolbarLayout
         mTabOrModelChangeRunnable = tabOrModelChangeRunnable;
     }
 
-    /** @param overlay The coordinator for the texture version of the top toolbar. */
-    void setOverlayCoordinator(TopToolbarOverlayCoordinator overlay) {
-        mOverlayCoordinator = overlay;
-        mOverlayCoordinator.setIsAndroidViewVisible(getVisibility() == View.VISIBLE);
+    /**
+     * @param callback Callback to invoke on visibility change of the texture version
+     *        of the top toolbar.
+     */
+    public void setOverlayVisibilityCallback(Callback<Boolean> callback) {
+        mOverlayVisibilityCallback = callback;
+        mOverlayVisibilityCallback.onResult(getVisibility() == View.VISIBLE);
     }
 
     @Override
     public void setVisibility(int visibility) {
         super.setVisibility(visibility);
-        if (mOverlayCoordinator != null) {
-            mOverlayCoordinator.setIsAndroidViewVisible(visibility == View.VISIBLE);
+        if (mOverlayVisibilityCallback != null) {
+            mOverlayVisibilityCallback.onResult(visibility == View.VISIBLE);
         }
     }
 

chrome/android/java/src/org/chromium/chrome/browser/toolbar/top/TopToolbarCoordinator.java

@@ -19,13 +19,7 @@ import org.chromium.base.supplier.OneShotCallback;
 import org.chromium.base.supplier.OneshotSupplier;
 import org.chromium.base.supplier.Supplier;
 import org.chromium.chrome.R;
-import org.chromium.chrome.browser.ActivityTabProvider;
 import org.chromium.chrome.browser.browser_controls.BrowserControlsStateProvider;
-import org.chromium.chrome.browser.compositor.Invalidator;
-import org.chromium.chrome.browser.compositor.overlays.toolbar.TopToolbarOverlayCoordinator;
-import org.chromium.chrome.browser.device.DeviceClassManager;
-import org.chromium.chrome.browser.findinpage.FindToolbar;
-import org.chromium.chrome.browser.layouts.LayoutManager;
 import org.chromium.chrome.browser.layouts.LayoutStateProvider;
 import org.chromium.chrome.browser.omnibox.LocationBar;
 import org.chromium.chrome.browser.tabmodel.IncognitoStateProvider;
@@ -88,7 +82,6 @@ public class TopToolbarCoordinator implements Toolbar {
     private MenuButtonCoordinator mMenuButtonCoordinator;
     private ObservableSupplier<AppMenuButtonHelper> mAppMenuButtonHelperSupplier;
     private ObservableSupplier<TabModelSelector> mTabModelSelectorSupplier;
-    private TopToolbarOverlayCoordinator mOverlayCoordinator;
 
     private Callback<ClipDrawableProgressBar.DrawingInfo> mProgressDrawInfoCallback;
     private ToolbarControlContainer mControlContainer;
@@ -185,15 +178,12 @@ public class TopToolbarCoordinator implements Toolbar {
      * @param newTabClickHandler The click handler for the new tab button.
      * @param bookmarkClickHandler The click handler for the bookmarks button.
      * @param customTabsBackClickHandler The click handler for the custom tabs back button.
-     * @param layoutManager A means of adding SceneOverlays.
-     * @param tabProvider A means of accessing the currently active tab.
      * @param browserControlsStateProvider Access to the state of the browser controls.
      */
     public void initializeWithNative(Runnable layoutUpdater,
             OnClickListener tabSwitcherClickHandler,
             OnLongClickListener tabSwitcherLongClickHandler, OnClickListener newTabClickHandler,
             OnClickListener bookmarkClickHandler, OnClickListener customTabsBackClickHandler,
-            LayoutManager layoutManager, ActivityTabProvider tabProvider,
             BrowserControlsStateProvider browserControlsStateProvider) {
         assert mTabModelSelectorSupplier.get() != null;
         if (mTabSwitcherModeCoordinatorPhone != null) {
@@ -218,16 +208,6 @@ public class TopToolbarCoordinator implements Toolbar {
         mToolbarLayout.setLayoutUpdater(layoutUpdater);
 
         mToolbarLayout.onNativeLibraryReady();
-
-        // If fullscreen is disabled, don't bother creating this overlay; only the android view will
-        // ever be shown.
-        if (DeviceClassManager.enableFullscreen()) {
-            mOverlayCoordinator = new TopToolbarOverlayCoordinator(mToolbarLayout.getContext(),
-                    layoutManager, mProgressDrawInfoCallback, tabProvider,
-                    browserControlsStateProvider, mResourceManagerSupplier);
-            layoutManager.addSceneOverlay(mOverlayCoordinator);
-            mToolbarLayout.setOverlayCoordinator(mOverlayCoordinator);
-        }
     }
 
     /**
@@ -255,11 +235,6 @@ public class TopToolbarCoordinator implements Toolbar {
      * Cleans up any code as necessary.
      */
     public void destroy() {
-        if (mOverlayCoordinator != null) {
-            mOverlayCoordinator.destroy();
-            mOverlayCoordinator = null;
-        }
-
         mToolbarLayout.destroy();
         if (mTabSwitcherModeCoordinatorPhone != null) {
             mTabSwitcherModeCoordinatorPhone.destroy();

chrome/android/javatests/src/org/chromium/chrome/browser/toolbar/load_progress/LoadProgressMediatorTest.java

@@ -23,13 +23,13 @@ import org.mockito.Mock;
 import org.mockito.MockitoAnnotations;
 
 import org.chromium.base.MathUtils;
+import org.chromium.base.supplier.ObservableSupplierImpl;
 import org.chromium.base.test.BaseJUnit4ClassRunner;
 import org.chromium.base.test.UiThreadTest;
 import org.chromium.base.test.util.Batch;
 import org.chromium.base.test.util.Criteria;
 import org.chromium.base.test.util.CriteriaHelper;
-import org.chromium.chrome.browser.ActivityTabProvider;
-import org.chromium.chrome.browser.ActivityTabProvider.ActivityTabObserver;
+import org.chromium.chrome.browser.tab.Tab;
 import org.chromium.chrome.browser.tab.TabImpl;
 import org.chromium.chrome.browser.tab.TabObserver;
 import org.chromium.chrome.browser.toolbar.load_progress.LoadProgressProperties.CompletionState;
@@ -44,8 +44,6 @@ public class LoadProgressMediatorTest {
     private static final String URL_1 = "http://starting.url";
     private static final String NATIVE_PAGE_URL = "chrome-native://newtab";
 
-    @Mock
-    public ActivityTabProvider mActivityTabProvider;
     @Mock
     private TabImpl mTab;
     @Mock
@@ -53,28 +51,32 @@ public class LoadProgressMediatorTest {
 
     @Captor
     public ArgumentCaptor<TabObserver> mTabObserverCaptor;
-    @Captor
-    public ArgumentCaptor<ActivityTabObserver> mActivityTabObserverCaptor;
 
     private PropertyModel mModel;
     private LoadProgressMediator mMediator;
     private TabObserver mTabObserver;
+    private ObservableSupplierImpl<Tab> mTabSupplier;
 
     @Before
     public void setUp() {
         MockitoAnnotations.initMocks(this);
-        when(mActivityTabProvider.get()).thenReturn(mTab);
-
         mModel = new PropertyModel(LoadProgressProperties.ALL_KEYS);
-        mMediator = new LoadProgressMediator(mActivityTabProvider, mModel);
-        verify(mActivityTabProvider).addObserver(mActivityTabObserverCaptor.capture());
+    }
+
+    private void initMediator() {
+        // ObservableSupplierImpl needs initialization in UI thread.
+        mTabSupplier = new ObservableSupplierImpl<>();
+        mMediator = new LoadProgressMediator(mTabSupplier, mModel);
+        mTabSupplier.set(mTab);
         verify(mTab).addObserver(mTabObserverCaptor.capture());
         mTabObserver = mTabObserverCaptor.getValue();
     }
 
     @Test
     @SmallTest
+    @UiThreadTest
     public void loadRegularPage() {
+        initMediator();
         assertEquals(mModel.get(LoadProgressProperties.COMPLETION_STATE),
                 CompletionState.FINISHED_DONT_ANIMATE);
 
@@ -96,10 +98,12 @@ public class LoadProgressMediatorTest {
 
     @Test
     @SmallTest
+    @UiThreadTest
     public void switchToLoadingTab() {
+        initMediator();
         doReturn(true).when(mTab2).isLoading();
         doReturn(0.1f).when(mTab2).getProgress();
-        mActivityTabObserverCaptor.getValue().onActivityTabChanged(mTab2, false);
+        mTabSupplier.set(mTab2);
         verify(mTab2, times(1)).addObserver(any());
 
         assertEquals(
@@ -109,7 +113,9 @@ public class LoadProgressMediatorTest {
 
     @Test
     @SmallTest
+    @UiThreadTest
     public void switchToLoadedTab() {
+        initMediator();
         NavigationHandle navigation = new NavigationHandle(0, new GURL(URL_1), true, false, false);
         mTabObserver.onDidStartNavigation(mTab, navigation);
         assertEquals(
@@ -117,7 +123,7 @@ public class LoadProgressMediatorTest {
         assertEquals(mModel.get(LoadProgressProperties.PROGRESS),
                 LoadProgressMediator.MINIMUM_LOAD_PROGRESS, MathUtils.EPSILON);
 
-        mActivityTabObserverCaptor.getValue().onActivityTabChanged(mTab2, false);
+        mTabSupplier.set(mTab2);
         verify(mTab2, times(1)).addObserver(any());
         assertEquals(mModel.get(LoadProgressProperties.COMPLETION_STATE),
                 CompletionState.FINISHED_DONT_ANIMATE);
@@ -125,7 +131,9 @@ public class LoadProgressMediatorTest {
 
     @Test
     @SmallTest
+    @UiThreadTest
     public void loadNativePage() {
+        initMediator();
         doReturn(0.1f).when(mTab).getProgress();
         NavigationHandle navigation = new NavigationHandle(0, new GURL(URL_1), true, false, false);
         mTabObserver.onDidStartNavigation(mTab, navigation);
@@ -141,7 +149,9 @@ public class LoadProgressMediatorTest {
 
     @Test
     @SmallTest
+    @UiThreadTest
     public void switchToTabWithNativePage() {
+        initMediator();
         NavigationHandle navigation = new NavigationHandle(0, new GURL(URL_1), true, false, false);
         mTabObserver.onDidStartNavigation(mTab, navigation);
         assertEquals(
@@ -150,7 +160,7 @@ public class LoadProgressMediatorTest {
                 LoadProgressMediator.MINIMUM_LOAD_PROGRESS, MathUtils.EPSILON);
 
         when(mTab2.getUrlString()).thenReturn(NATIVE_PAGE_URL);
-        mActivityTabObserverCaptor.getValue().onActivityTabChanged(mTab2, false);
+        mTabSupplier.set(mTab2);
         verify(mTab2, times(1)).addObserver(any());
         assertEquals(mModel.get(LoadProgressProperties.COMPLETION_STATE),
                 CompletionState.FINISHED_DONT_ANIMATE);
@@ -160,7 +170,9 @@ public class LoadProgressMediatorTest {
 
     @Test
     @SmallTest
+    @UiThreadTest
     public void pageCrashes() {
+        initMediator();
         NavigationHandle navigation = new NavigationHandle(0, new GURL(URL_1), true, false, false);
         mTabObserver.onDidStartNavigation(mTab, navigation);
         assertEquals(
@@ -179,6 +191,7 @@ public class LoadProgressMediatorTest {
     @SmallTest
     @UiThreadTest
     public void testSwapWebContents() {
+        initMediator();
         assertEquals(mModel.get(LoadProgressProperties.COMPLETION_STATE),
                 CompletionState.FINISHED_DONT_ANIMATE);
         mTabObserver.onWebContentsSwapped(mTab, true, true);
@@ -201,7 +214,9 @@ public class LoadProgressMediatorTest {
 
     @Test
     @SmallTest
+    @UiThreadTest
     public void testSameDocumentLoad_afterFinishedLoading() {
+        initMediator();
         GURL gurl = new GURL(URL_1);
         assertEquals(mModel.get(LoadProgressProperties.COMPLETION_STATE),
                 CompletionState.FINISHED_DONT_ANIMATE);

chrome/android/junit/src/org/chromium/chrome/browser/toolbar/top/HomeButtonCoordinatorTest.java

@@ -27,14 +27,15 @@ import org.robolectric.annotation.Config;
 import org.robolectric.annotation.Implementation;
 import org.robolectric.annotation.Implements;
 
+import org.chromium.base.supplier.ObservableSupplierImpl;
 import org.chromium.base.supplier.OneshotSupplierImpl;
 import org.chromium.base.test.BaseRobolectricTestRunner;
 import org.chromium.chrome.R;
-import org.chromium.chrome.browser.ActivityTabProvider;
 import org.chromium.chrome.browser.feed.shared.FeedFeatures;
 import org.chromium.chrome.browser.flags.ChromeFeatureList;
 import org.chromium.chrome.browser.homepage.HomepageManager;
 import org.chromium.chrome.browser.intent.IntentMetadata;
+import org.chromium.chrome.browser.tab.Tab;
 import org.chromium.chrome.browser.toolbar.HomeButton;
 import org.chromium.chrome.browser.user_education.IPHCommand;
 import org.chromium.chrome.browser.user_education.UserEducationHelper;
@@ -106,8 +107,6 @@ public class HomeButtonCoordinatorTest {
     @Mock
     private Context mContext;
     @Mock
-    private ActivityTabProvider mActivityTabProvider;
-    @Mock
     private HomeButton mHomeButton;
     @Mock
     private android.content.res.Resources mResources;
@@ -140,9 +139,9 @@ public class HomeButtonCoordinatorTest {
 
     private HomeButtonCoordinator newHomeButtonCoordinator(View view) {
         // clang-format off
-        return new HomeButtonCoordinator(mContext, view, mActivityTabProvider, mUserEducationHelper,
-                () -> mIsIncognito, mIntentMetadataOneshotSupplier, mPromoShownOneshotSupplier,
-                HomepageManager::isHomepageNonNtp);
+        return new HomeButtonCoordinator(mContext, view, mUserEducationHelper, () -> mIsIncognito,
+                mIntentMetadataOneshotSupplier, mPromoShownOneshotSupplier,
+                HomepageManager::isHomepageNonNtp, new ObservableSupplierImpl<Tab>());
         // clang-format on
     }
 

chrome/android/junit/src/org/chromium/chrome/browser/toolbar/top/ToggleTabStackButtonCoordinatorTest.java

@@ -27,13 +27,14 @@ import org.robolectric.annotation.Implementation;
 import org.robolectric.annotation.Implements;
 
 import org.chromium.base.Callback;
+import org.chromium.base.supplier.ObservableSupplierImpl;
 import org.chromium.base.supplier.OneshotSupplierImpl;
 import org.chromium.base.test.BaseRobolectricTestRunner;
-import org.chromium.chrome.browser.ActivityTabProvider;
 import org.chromium.chrome.browser.flags.ChromeFeatureList;
 import org.chromium.chrome.browser.intent.IntentMetadata;
 import org.chromium.chrome.browser.layouts.LayoutStateProvider;
 import org.chromium.chrome.browser.layouts.LayoutType;
+import org.chromium.chrome.browser.tab.Tab;
 import org.chromium.chrome.browser.user_education.IPHCommand;
 import org.chromium.chrome.browser.user_education.UserEducationHelper;
 import org.chromium.components.feature_engagement.FeatureConstants;
@@ -67,8 +68,6 @@ public class ToggleTabStackButtonCoordinatorTest {
     @Mock
     private Context mContext;
     @Mock
-    private ActivityTabProvider mActivityTabProvider;
-    @Mock
     private LayoutStateProvider mLayoutStateProvider;
     @Mock
     private ToggleTabStackButton mToggleTabStackButton;
@@ -124,12 +123,12 @@ public class ToggleTabStackButtonCoordinatorTest {
 
     private ToggleTabStackButtonCoordinator newToggleTabStackButtonCoordinator(
             ToggleTabStackButton toggleTabStackButton) {
+        // clang-format off
         return new ToggleTabStackButtonCoordinator(mContext, toggleTabStackButton,
-                mActivityTabProvider, mUserEducationHelper,
-                ()
-                        -> mIsIncognito,
-                mIntentMetadataOneshotSupplier, mPromoShownOneshotSupplier,
-                mLayoutSateProviderOneshotSupplier, mSetNewTabButtonHighlightCallback);
+                mUserEducationHelper, () -> mIsIncognito, mIntentMetadataOneshotSupplier,
+                mPromoShownOneshotSupplier, mLayoutSateProviderOneshotSupplier,
+                mSetNewTabButtonHighlightCallback, new ObservableSupplierImpl<Tab>());
+        // clang-format on
     }
 
     private void showOverviewMode() {

chrome/browser/tab/BUILD.gn

@@ -8,6 +8,7 @@ import("//chrome/browser/buildflags.gni")
 
 android_library("java") {
   sources = [
+    "java/src/org/chromium/chrome/browser/tab/CurrentTabObserver.java",
     "java/src/org/chromium/chrome/browser/tab/EmptyTabObserver.java",
     "java/src/org/chromium/chrome/browser/tab/Tab.java",
     "java/src/org/chromium/chrome/browser/tab/TabAttributeKeys.java",

chrome/browser/tab/java/src/org/chromium/chrome/browser/tab/CurrentTabObserver.java

+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.chrome.browser.tab;
+
+import androidx.annotation.NonNull;
+
+import org.chromium.base.Callback;
+import org.chromium.base.CallbackController;
+import org.chromium.base.supplier.ObservableSupplier;
+
+/**
+ * TabObserver that keeps switching to always observe the current tab. A stop-gap solution
+ * to ActivityTabTabObserver for classes that cannot reference it directly.
+ * TODO(crbug.com/1146871): Just switch to ActivityTabTabObserver once ActivityTabProvider
+ *                  gets modularized.
+ */
+public class CurrentTabObserver {
+    private final ObservableSupplier<Tab> mTabSupplier;
+    private final TabObserver mTabObserver;
+    private final Callback<Tab> mTabSupplierCallback;
+
+    private CallbackController mCallbackController;
+    private Tab mTab;
+
+    /**
+     * @param tabSupplier An observable supplier of the current {@link Tab}. NOT to be owned
+     *        by this class, and should be destroyed by callsite later.
+     * @param tabObserver {@link TabObserver} that we want to observe the current tab with.
+     *        Owned by this class.
+     */
+    public CurrentTabObserver(
+            @NonNull ObservableSupplier<Tab> tabSupplier, @NonNull TabObserver tabObserver) {
+        mTabSupplier = tabSupplier;
+        mTabObserver = tabObserver;
+        mCallbackController = new CallbackController();
+        mTabSupplierCallback = mCallbackController.makeCancelable((tab) -> {
+            if (mTab != null) mTab.removeObserver(mTabObserver);
+            mTab = tab;
+            if (mTab != null) mTab.addObserver(mTabObserver);
+        });
+        mTabSupplier.addObserver(mTabSupplierCallback);
+    }
+
+    /** Destroy the current tab observer. This should be called after use. */
+    public void destroy() {
+        if (mTab != null) mTab.removeObserver(mTabObserver);
+        mTabSupplier.removeObserver(mTabSupplierCallback);
+        mCallbackController.destroy();
+        mCallbackController = null;
+    }
+}