Android: Factor out accessibility handling out of ChromeActivity

This CL factors accessibility-related methods/interfaces out of
ChromeActivity into its own class ChromeAccessibility.
|updateAccessibiilityVisibility| in TabImpl was also moved to
the new class, reducing the ChromeActivity's dependency
on TabImpl.

Bug: 995903
Change-Id: I2296aa25cbcee3e09f1fa48a5ba43ccb9eec92ed
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2015919
Commit-Queue: Jinsuk Kim <jinsukkim@chromium.org>
Reviewed-by: Matthew Jones <mdjones@chromium.org>
Reviewed-by: Theresa  <twellington@chromium.org>
Cr-Commit-Position: refs/heads/master@{#740464}

chrome/android/java/src/org/chromium/chrome/browser/ChromeActivity.java

@@ -28,9 +28,6 @@ import android.view.View;
 import android.view.ViewGroup;
 import android.view.ViewStub;
 import android.view.WindowManager;
-import android.view.accessibility.AccessibilityManager;
-import android.view.accessibility.AccessibilityManager.AccessibilityStateChangeListener;
-import android.view.accessibility.AccessibilityManager.TouchExplorationStateChangeListener;
 
 import androidx.annotation.CallSuper;
 import androidx.annotation.NonNull;
@@ -92,7 +89,6 @@ import org.chromium.chrome.browser.gsa.GSAAccountChangeListener;
 import org.chromium.chrome.browser.gsa.GSAState;
 import org.chromium.chrome.browser.help.HelpAndFeedback;
 import org.chromium.chrome.browser.history.HistoryManagerUtils;
-import org.chromium.chrome.browser.infobar.InfoBarContainer;
 import org.chromium.chrome.browser.init.AsyncInitializationActivity;
 import org.chromium.chrome.browser.init.ProcessInitializationHandler;
 import org.chromium.chrome.browser.init.StartupTabPreloader;
@@ -125,6 +121,7 @@ import org.chromium.chrome.browser.share.ShareDelegate;
 import org.chromium.chrome.browser.share.ShareDelegateImpl;
 import org.chromium.chrome.browser.sync.ProfileSyncService;
 import org.chromium.chrome.browser.sync.SyncController;
+import org.chromium.chrome.browser.tab.AccessibilityVisibilityHandler;
 import org.chromium.chrome.browser.tab.Tab;
 import org.chromium.chrome.browser.tab.TabDelegateFactory;
 import org.chromium.chrome.browser.tab.TabHidingType;
@@ -152,7 +149,6 @@ import org.chromium.chrome.browser.ui.appmenu.AppMenuPropertiesDelegate;
 import org.chromium.chrome.browser.ui.messages.snackbar.SnackbarManager;
 import org.chromium.chrome.browser.ui.messages.snackbar.SnackbarManager.SnackbarManageable;
 import org.chromium.chrome.browser.ui.system.StatusBarColorController;
-import org.chromium.chrome.browser.util.AccessibilityUtil;
 import org.chromium.chrome.browser.vr.ArDelegate;
 import org.chromium.chrome.browser.vr.ArDelegateProvider;
 import org.chromium.chrome.browser.vr.VrModuleProvider;
@@ -201,8 +197,8 @@ import java.util.function.Consumer;
  */
 public abstract class ChromeActivity<C extends ChromeActivityComponent>
         extends AsyncInitializationActivity
-        implements TabCreatorManager, AccessibilityStateChangeListener, PolicyChangeListener,
-                   ContextualSearchTabPromotionDelegate, SnackbarManageable, SceneChangeObserver,
+        implements TabCreatorManager, PolicyChangeListener, ContextualSearchTabPromotionDelegate,
+                   SnackbarManageable, SceneChangeObserver,
                    StatusBarColorController.StatusBarColorProvider, AppMenuDelegate, AppMenuBlocker,
                    MenuOrKeyboardActionController {
     /**
@@ -245,12 +241,7 @@ public abstract class ChromeActivity<C extends ChromeActivityComponent>
     private boolean mTabModelsInitialized;
     private boolean mNativeInitialized;
     private boolean mRemoveWindowBackgroundDone;
-
-    // The class cannot implement TouchExplorationStateChangeListener,
-    // because it is only available for Build.VERSION_CODES.KITKAT and later.
-    // We have to instantiate the TouchExplorationStateChangeListner object in the code.
-    @SuppressLint("NewApi")
-    private TouchExplorationStateChangeListener mTouchExplorationStateChangeListener;
+    protected AccessibilityVisibilityHandler mAccessibilityVisibilityHandler;
 
     // Observes when sync becomes ready to create the mContextReporter.
     private ProfileSyncService.SyncStateChangedListener mSyncStateChangedListener;
@@ -422,15 +413,6 @@ public abstract class ChromeActivity<C extends ChromeActivityComponent>
                 mAssistStatusHandler.updateAssistState();
             }
 
-            AccessibilityManager manager = (AccessibilityManager) getBaseContext().getSystemService(
-                    Context.ACCESSIBILITY_SERVICE);
-            manager.addAccessibilityStateChangeListener(this);
-            mTouchExplorationStateChangeListener = enabled -> {
-                AccessibilityUtil.resetAccessibilityEnabled();
-                checkAccessibility();
-            };
-            manager.addTouchExplorationStateChangeListener(mTouchExplorationStateChangeListener);
-
             // Make the activity listen to policy change events
             CombinedPolicyProvider.get().addPolicyChangeListener(this);
             mDidAddPolicyChangeListener = true;
@@ -1128,11 +1110,6 @@ public abstract class ChromeActivity<C extends ChromeActivityComponent>
         }
         if (mCompositorViewHolder != null) mCompositorViewHolder.onStart();
 
-        // Explicitly call checkAccessibility() so things are initialized correctly when Chrome has
-        // been re-started after closing due to the last tab being closed when homepage is enabled.
-        // See crbug.com/541546.
-        checkAccessibility();
-
         Configuration config = getResources().getConfiguration();
         mUiMode = config.uiMode;
         mDensityDpi = config.densityDpi;
@@ -1267,11 +1244,6 @@ public abstract class ChromeActivity<C extends ChromeActivityComponent>
 
         UpdateMenuItemHelper.getInstance().unregisterObserver(mUpdateStateChangedListener);
 
-        AccessibilityManager manager = (AccessibilityManager)
-                getBaseContext().getSystemService(Context.ACCESSIBILITY_SERVICE);
-        manager.removeAccessibilityStateChangeListener(this);
-        manager.removeTouchExplorationStateChangeListener(mTouchExplorationStateChangeListener);
-
         mActivityTabProvider.destroy();
 
         mComponent = null;
@@ -1407,23 +1379,6 @@ public abstract class ChromeActivity<C extends ChromeActivityComponent>
         return mNativeInitialized;
     }
 
-    /**
-     * Called when the accessibility status of this device changes.  This might be triggered by
-     * touch exploration or general accessibility status updates.  It is an aggregate of two other
-     * accessibility update methods.
-     *
-     * @see #onAccessibilityStateChanged
-     * @see #mTouchExplorationStateChangeListener
-     * @param enabled Whether or not accessibility and touch exploration are currently enabled.
-     */
-    protected void onAccessibilityModeChanged(boolean enabled) {
-        InfoBarContainer.setIsAllowedToAutoHide(!enabled);
-        if (getToolbarManager() != null) getToolbarManager().onAccessibilityStatusChanged(enabled);
-        if (mContextualSearchManager != null) {
-            mContextualSearchManager.onAccessibilityModeChanged(enabled);
-        }
-    }
-
     @Override
     public boolean onOptionsItemSelected(int itemId, @Nullable Bundle menuItemData) {
         if (mManualFillingComponent != null) mManualFillingComponent.dismiss();
@@ -1480,16 +1435,6 @@ public abstract class ChromeActivity<C extends ChromeActivityComponent>
         };
     }
 
-    @Override
-    public final void onAccessibilityStateChanged(boolean enabled) {
-        AccessibilityUtil.resetAccessibilityEnabled();
-        checkAccessibility();
-    }
-
-    private void checkAccessibility() {
-        onAccessibilityModeChanged(AccessibilityUtil.isAccessibilityEnabled());
-    }
-
     /**
      * @return A casted version of {@link #getApplication()}.
      */

chrome/android/java/src/org/chromium/chrome/browser/ChromeTabbedActivity.java

@@ -170,7 +170,7 @@ import java.util.Locale;
  * This is the main activity for ChromeMobile when not running in document mode.  All the tabs
  * are accessible via a chrome specific tab switching UI.
  */
-public class ChromeTabbedActivity extends ChromeActivity {
+public class ChromeTabbedActivity extends ChromeActivity implements AccessibilityUtil.Observer {
     private static final String TAG = "ChromeTabbedActivity";
 
     private static final String HELP_URL_PREFIX = "https://support.google.com/chrome/";
@@ -826,6 +826,7 @@ public class ChromeTabbedActivity extends ChromeActivity {
                     this::maybeGetFeedAppLifecycleAndMaybeCreatePageViewObserver);
             PostTask.postTask(UiThreadTaskTraits.DEFAULT, this::addOverviewModeObserver);
             PostTask.postTask(UiThreadTaskTraits.DEFAULT, this::finishNativeInitialization);
+            AccessibilityUtil.addObserver(this);
         }
     }
 
@@ -838,6 +839,9 @@ public class ChromeTabbedActivity extends ChromeActivity {
         mOverviewListLayout = (OverviewListLayout) mLayoutManager.getOverviewListLayout();
         getTabObscuringHandler().addObserver(mCompositorViewHolder);
         getTabObscuringHandler().addObserver(mOverviewListLayout);
+
+        AccessibilityUtil.addObserver(mLayoutManager);
+        if (isTablet()) AccessibilityUtil.addObserver(mCompositorViewHolder);
     }
 
     @Override
@@ -1169,17 +1173,6 @@ public class ChromeTabbedActivity extends ChromeActivity {
 
     @Override
     public void onAccessibilityModeChanged(boolean enabled) {
-        super.onAccessibilityModeChanged(enabled);
-
-        if (mLayoutManager != null) {
-            mLayoutManager.setEnableAnimations(DeviceClassManager.enableAnimations());
-        }
-        if (isTablet()) {
-            if (getCompositorViewHolder() != null) {
-                getCompositorViewHolder().onAccessibilityStatusChanged(enabled);
-            }
-        }
-
         onAccessibilityTabSwitcherModeChanged();
     }
 
@@ -2024,6 +2017,10 @@ public class ChromeTabbedActivity extends ChromeActivity {
             getTabObscuringHandler().removeObserver(mOverviewListLayout);
         }
 
+        if (isTablet()) AccessibilityUtil.removeObserver(mCompositorViewHolder);
+        AccessibilityUtil.removeObserver(this);
+        AccessibilityUtil.removeObserver(mLayoutManager);
+
         super.onDestroyInternal();
     }
 

chrome/android/java/src/org/chromium/chrome/browser/compositor/CompositorViewHolder.java

@@ -59,6 +59,7 @@ import org.chromium.chrome.browser.tabmodel.TabModelSelector;
 import org.chromium.chrome.browser.toolbar.ControlContainer;
 import org.chromium.chrome.browser.toolbar.ToolbarColors;
 import org.chromium.chrome.browser.ui.TabObscuringHandler;
+import org.chromium.chrome.browser.util.AccessibilityUtil;
 import org.chromium.components.browser_ui.widget.InsetObserverView;
 import org.chromium.components.content_capture.ContentCaptureConsumer;
 import org.chromium.components.content_capture.ContentCaptureConsumerImpl;
@@ -86,7 +87,8 @@ import java.util.Set;
 public class CompositorViewHolder extends FrameLayout
         implements ContentOffsetProvider, LayoutManagerHost, LayoutRenderHost, Invalidator.Host,
                    FullscreenListener, InsetObserverView.WindowInsetObserver,
-                   CompositorViewResizer.Observer, TabObscuringHandler.Observer {
+                   CompositorViewResizer.Observer, AccessibilityUtil.Observer,
+                   TabObscuringHandler.Observer {
     private static final long SYSTEM_UI_VIEWPORT_UPDATE_DELAY_MS = 500;
 
     /**
@@ -1300,14 +1302,14 @@ public class CompositorViewHolder extends FrameLayout
         }
     }
 
-    /**
-     * Called when the accessibility enabled state changes.
-     * @param enabled Whether accessibility is enabled.
-     */
-    public void onAccessibilityStatusChanged(boolean enabled) {
+    // AccessibilityUtil.Observer
+
+    @Override
+    public void onAccessibilityModeChanged(boolean enabled) {
         // Instantiate and install the accessibility node provider on this view if necessary.
         // This overrides any hover event listeners or accessibility delegates
         // that may have been added elsewhere.
+        assert mLayoutManager != null;
         if (enabled && (mNodeProvider == null)) {
             mAccessibilityView = new View(getContext());
             addView(mAccessibilityView);

chrome/android/java/src/org/chromium/chrome/browser/compositor/layouts/LayoutManagerChrome.java

@@ -45,7 +45,8 @@ import java.util.List;
  * A {@link Layout} controller for the more complicated Chrome browser.  This is currently a
  * superset of {@link LayoutManager}.
  */
-public class LayoutManagerChrome extends LayoutManager implements OverviewModeController {
+public class LayoutManagerChrome
+        extends LayoutManager implements OverviewModeController, AccessibilityUtil.Observer {
     // Layouts
     /** An {@link Layout} that should be used as the accessibility tab switcher. */
     protected OverviewListLayout mOverviewListLayout;
@@ -414,6 +415,13 @@ public class LayoutManagerChrome extends LayoutManager implements OverviewModeCo
         mOverviewModeObservers.removeObserver(listener);
     }
 
+    // AccessibilityUtil.Observer
+
+    @Override
+    public void onAccessibilityModeChanged(boolean enabled) {
+        setEnableAnimations(DeviceClassManager.enableAnimations());
+    }
+
     /**
      * A {@link EdgeSwipeHandler} meant to respond to edge events for the toolbar.
      */

chrome/android/java/src/org/chromium/chrome/browser/contextualsearch/ContextualSearchManager.java

@@ -53,6 +53,7 @@ import org.chromium.chrome.browser.tab.TabSelectionType;
 import org.chromium.chrome.browser.tabmodel.TabModelSelector;
 import org.chromium.chrome.browser.tabmodel.TabModelSelectorTabModelObserver;
 import org.chromium.chrome.browser.tabmodel.TabModelSelectorTabObserver;
+import org.chromium.chrome.browser.util.AccessibilityUtil;
 import org.chromium.components.feature_engagement.EventConstants;
 import org.chromium.components.feature_engagement.FeatureConstants;
 import org.chromium.components.feature_engagement.Tracker;
@@ -77,9 +78,9 @@ import java.util.regex.Pattern;
  * Manager for the Contextual Search feature. This class keeps track of the status of Contextual
  * Search and coordinates the control with the layout.
  */
-public class ContextualSearchManager implements ContextualSearchManagementDelegate,
-                                                ContextualSearchNetworkCommunicator,
-                                                ContextualSearchSelectionHandler {
+public class ContextualSearchManager
+        implements ContextualSearchManagementDelegate, ContextualSearchNetworkCommunicator,
+                   ContextualSearchSelectionHandler, AccessibilityUtil.Observer {
     /** A delegate for reporting selected context to GSA for search quality. */
     public interface ContextReporterDelegate {
         /**
@@ -287,6 +288,7 @@ public class ContextualSearchManager implements ContextualSearchManagementDelega
         mInternalStateController.reset(StateChangeReason.UNKNOWN);
 
         listenForTabModelSelectorNotifications();
+        AccessibilityUtil.addObserver(this);
     }
 
     /**
@@ -303,6 +305,7 @@ public class ContextualSearchManager implements ContextualSearchManagementDelega
         stopListeningForHideNotifications();
         mTabRedirectHandler.clear();
         mInternalStateController.enter(InternalState.UNDEFINED);
+        AccessibilityUtil.removeObserver(this);
     }
 
     @Override
@@ -879,11 +882,7 @@ public class ContextualSearchManager implements ContextualSearchManagementDelega
         }
     }
 
-    /**
-     * Notifies that the Accessibility Mode state has changed.
-     *
-     * @param enabled Whether the Accessibility Mode is enabled.
-     */
+    @Override
     public void onAccessibilityModeChanged(boolean enabled) {
         mIsAccessibilityModeEnabled = enabled;
         if (enabled) hideContextualSearch(StateChangeReason.UNKNOWN);

chrome/android/java/src/org/chromium/chrome/browser/infobar/InfoBarContainer.java

@@ -22,6 +22,7 @@ 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.ui.messages.snackbar.SnackbarManager;
+import org.chromium.chrome.browser.util.AccessibilityUtil;
 import org.chromium.chrome.browser.widget.bottomsheet.BottomSheetController;
 import org.chromium.chrome.browser.widget.bottomsheet.BottomSheetObserver;
 import org.chromium.chrome.browser.widget.bottomsheet.EmptyBottomSheetObserver;
@@ -42,6 +43,13 @@ public class InfoBarContainer implements UserData, KeyboardVisibilityListener {
 
     private static final Class<InfoBarContainer> USER_DATA_KEY = InfoBarContainer.class;
 
+    private static final AccessibilityUtil.Observer sAccessibilityObserver;
+
+    static {
+        sAccessibilityObserver = (enabled) -> setIsAllowedToAutoHide(!enabled);
+        AccessibilityUtil.addObserver(sAccessibilityObserver);
+    }
+
     /**
      * A listener for the InfoBar animations.
      */
@@ -426,7 +434,7 @@ public class InfoBarContainer implements UserData, KeyboardVisibilityListener {
      * Expected to be called when Touch Exploration is enabled.
      * @param isAllowed Whether auto-hiding is allowed.
      */
-    public static void setIsAllowedToAutoHide(boolean isAllowed) {
+    private static void setIsAllowedToAutoHide(boolean isAllowed) {
         InfoBarContainerView.setIsAllowedToAutoHide(isAllowed);
     }
 

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

@@ -109,6 +109,7 @@ import org.chromium.chrome.browser.ui.appmenu.AppMenuObserver;
 import org.chromium.chrome.browser.ui.appmenu.AppMenuPropertiesDelegate;
 import org.chromium.chrome.browser.ui.appmenu.MenuButtonDelegate;
 import org.chromium.chrome.browser.ui.native_page.NativePage;
+import org.chromium.chrome.browser.util.AccessibilityUtil;
 import org.chromium.chrome.browser.util.UrlConstants;
 import org.chromium.chrome.browser.widget.ScrimView;
 import org.chromium.chrome.browser.widget.ScrimView.ScrimObserver;
@@ -137,7 +138,8 @@ import java.util.List;
  * with the rest of the application to ensure the toolbar is always visually up to date.
  */
 public class ToolbarManager implements ScrimObserver, ToolbarTabController, UrlFocusChangeListener,
-                                       ThemeColorObserver, MenuButtonDelegate {
+                                       ThemeColorObserver, MenuButtonDelegate,
+                                       AccessibilityUtil.Observer {
     /**
      * Handle UI updates of menu icons. Only applicable for phones.
      */
@@ -753,6 +755,8 @@ public class ToolbarManager implements ScrimObserver, ToolbarTabController, UrlF
         mToolbar.setIncognitoStateProvider(mIncognitoStateProvider);
         mToolbar.setThemeColorProvider(
                 mActivity.isTablet() ? mAppThemeColorProvider : mTabThemeColorProvider);
+
+        AccessibilityUtil.addObserver(this);
     }
 
     /**
@@ -1214,6 +1218,7 @@ public class ToolbarManager implements ScrimObserver, ToolbarTabController, UrlF
         if (mAppThemeColorProvider != null) mAppThemeColorProvider.destroy();
         mActivity.unregisterComponentCallbacks(mComponentCallbacks);
         mComponentCallbacks = null;
+        AccessibilityUtil.removeObserver(this);
     }
 
     /**
@@ -1245,11 +1250,8 @@ public class ToolbarManager implements ScrimObserver, ToolbarTabController, UrlF
         }
     }
 
-    /**
-     * Called when the accessibility enabled state changes.
-     * @param enabled Whether accessibility is enabled.
-     */
-    public void onAccessibilityStatusChanged(boolean enabled) {
+    @Override
+    public void onAccessibilityModeChanged(boolean enabled) {
         mToolbar.onAccessibilityStatusChanged(enabled);
     }
 

chrome/browser/util/android/java/src/org/chromium/chrome/browser/util/AccessibilityUtil.java

@@ -10,6 +10,8 @@ import android.content.Context;
 import android.content.res.Configuration;
 import android.os.Build;
 import android.view.accessibility.AccessibilityManager;
+import android.view.accessibility.AccessibilityManager.AccessibilityStateChangeListener;
+import android.view.accessibility.AccessibilityManager.TouchExplorationStateChangeListener;
 
 import androidx.annotation.Nullable;
 import androidx.annotation.VisibleForTesting;
@@ -18,6 +20,7 @@ import org.chromium.base.ActivityState;
 import org.chromium.base.ApplicationStatus;
 import org.chromium.base.ApplicationStatus.ActivityStateListener;
 import org.chromium.base.ContextUtils;
+import org.chromium.base.ObserverList;
 import org.chromium.base.TraceEvent;
 
 import java.util.List;
@@ -26,8 +29,41 @@ import java.util.List;
  * Exposes information about the current accessibility state
  */
 public class AccessibilityUtil {
+    /**
+     * An observer to be notified of accessibility status changes.
+     */
+    public interface Observer {
+        /**
+         * @param enabled Whether a touch exploration or an accessibility service that performs can
+         *        perform gestures is enabled. Indicates that the UI must be fully navigable using
+         *        the accessibility view tree.
+         */
+        void onAccessibilityModeChanged(boolean enabled);
+    }
+
     private static Boolean sIsAccessibilityEnabled;
     private static ActivityStateListener sActivityStateListener;
+    private static ObserverList<Observer> sObservers;
+    private static class ModeChangeHandler
+            implements AccessibilityStateChangeListener, TouchExplorationStateChangeListener {
+        // AccessibilityStateChangeListener
+
+        @Override
+        public final void onAccessibilityStateChanged(boolean enabled) {
+            resetAccessibilityEnabled();
+            notifyModeChange();
+        }
+
+        // TouchExplorationStateChangeListener
+
+        @Override
+        public void onTouchExplorationStateChanged(boolean enabled) {
+            resetAccessibilityEnabled();
+            notifyModeChange();
+        }
+    }
+
+    private static ModeChangeHandler sModeChangeHandler;
 
     private AccessibilityUtil() {}
 
@@ -36,13 +72,12 @@ public class AccessibilityUtil {
      * @return        Whether or not accessibility and touch exploration are enabled.
      */
     public static boolean isAccessibilityEnabled() {
+        if (sModeChangeHandler == null) registerModeChangeListeners();
         if (sIsAccessibilityEnabled != null) return sIsAccessibilityEnabled;
 
         TraceEvent.begin("AccessibilityManager::isAccessibilityEnabled");
 
-        AccessibilityManager manager =
-                (AccessibilityManager) ContextUtils.getApplicationContext().getSystemService(
-                        Context.ACCESSIBILITY_SERVICE);
+        AccessibilityManager manager = getAccessibilityManager();
         boolean accessibilityEnabled =
                 manager != null && manager.isEnabled() && manager.isTouchExplorationEnabled();
 
@@ -72,6 +107,7 @@ public class AccessibilityUtil {
                         || ApplicationStatus.isEveryActivityDestroyed()) {
                     resetAccessibilityEnabled();
                 }
+                if (ApplicationStatus.isEveryActivityDestroyed()) cleanUp();
             }
         };
         ApplicationStatus.registerStateListenerForAllActivities(sActivityStateListener);
@@ -80,23 +116,78 @@ public class AccessibilityUtil {
         return sIsAccessibilityEnabled;
     }
 
+    /**
+     * Add {@link Observer} object. The observer will be notified of the current accessibility
+     * mode immediately.
+     * @param observer Observer object monitoring a11y mode change.
+     */
+    public static void addObserver(Observer observer) {
+        getObservers().addObserver(observer);
+
+        // Notify mode change to a new observer so things are initialized correctly when Chrome
+        // has been re-started after closing due to the last tab being closed when homepage is
+        // enabled. See crbug.com/541546.
+        observer.onAccessibilityModeChanged(isAccessibilityEnabled());
+    }
+
+    /**
+     * Remove {@link Observer} object.
+     * @param observer Observer object monitoring a11y mode change.
+     */
+    public static void removeObserver(Observer observer) {
+        getObservers().removeObserver(observer);
+    }
+
+    /**
+     * @return True if a hardware keyboard is detected.
+     */
+    public static boolean isHardwareKeyboardAttached(Configuration c) {
+        return c.keyboard != Configuration.KEYBOARD_NOKEYS;
+    }
+
+    private static AccessibilityManager getAccessibilityManager() {
+        return (AccessibilityManager) ContextUtils.getApplicationContext().getSystemService(
+                Context.ACCESSIBILITY_SERVICE);
+    }
+
+    private static void registerModeChangeListeners() {
+        assert sModeChangeHandler == null;
+        sModeChangeHandler = new ModeChangeHandler();
+        AccessibilityManager manager = getAccessibilityManager();
+        manager.addAccessibilityStateChangeListener(sModeChangeHandler);
+        manager.addTouchExplorationStateChangeListener(sModeChangeHandler);
+    }
+
+    private static void cleanUp() {
+        if (sObservers != null) sObservers.clear();
+        if (sModeChangeHandler == null) return;
+        AccessibilityManager manager = getAccessibilityManager();
+        manager.removeAccessibilityStateChangeListener(sModeChangeHandler);
+        manager.removeTouchExplorationStateChangeListener(sModeChangeHandler);
+    }
+
     /**
      * Reset the static used to determine whether accessibility is enabled.
-     * TODO(twellington): Make this private and have classes that care about accessibility state
-     *                    observe this class rather than observing the AccessibilityManager
-     *                    directly.
      */
-    public static void resetAccessibilityEnabled() {
+    private static void resetAccessibilityEnabled() {
         ApplicationStatus.unregisterActivityStateListener(sActivityStateListener);
         sActivityStateListener = null;
         sIsAccessibilityEnabled = null;
     }
 
+    private static ObserverList<Observer> getObservers() {
+        if (sObservers == null) sObservers = new ObserverList<>();
+        return sObservers;
+    }
+
     /**
-     * @return True if a hardware keyboard is detected.
+     * Notify all the observers of the mode change.
      */
-    public static boolean isHardwareKeyboardAttached(Configuration c) {
-        return c.keyboard != Configuration.KEYBOARD_NOKEYS;
+    private static void notifyModeChange() {
+        boolean enabled = isAccessibilityEnabled();
+        for (Observer observer : getObservers()) {
+            observer.onAccessibilityModeChanged(enabled);
+        }
     }
 
     /**