[Start Surface] Add and remove TabmodelSelectorObserver with Overview.

Bug: 982018

Change-Id: If3abc60b1a7f911e76a655886979d572664c9abe
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1930142Reviewed-by: Yusuf Ozuysal <yusufo@chromium.org>
Commit-Queue: Mia Glaese <glamia@chromium.org>
Cr-Commit-Position: refs/heads/master@{#719214}

chrome/android/features/start_surface/internal/java/src/org/chromium/chrome/features/start_surface/StartSurfaceMediator.java

@@ -39,6 +39,7 @@ import org.chromium.chrome.browser.tabmodel.EmptyTabModelSelectorObserver;
 import org.chromium.chrome.browser.tabmodel.TabModel;
 import org.chromium.chrome.browser.tabmodel.TabModelObserver;
 import org.chromium.chrome.browser.tabmodel.TabModelSelector;
+import org.chromium.chrome.browser.tabmodel.TabModelSelectorObserver;
 import org.chromium.chrome.browser.tasks.tab_management.TabSwitcher;
 import org.chromium.chrome.start_surface.R;
 import org.chromium.ui.modelutil.PropertyModel;
@@ -96,6 +97,8 @@ class StartSurfaceMediator
     private TabModel mNormalTabModel;
     @Nullable
     private TabModelObserver mNormalTabModelObserver;
+    @Nullable
+    private TabModelSelectorObserver mTabModelSelectorObserver;
 
     StartSurfaceMediator(TabSwitcher.Controller controller, TabModelSelector tabModelSelector,
             @Nullable PropertyModel propertyModel,
@@ -119,14 +122,14 @@ class StartSurfaceMediator
 
             mIsIncognito = mTabModelSelector.isIncognitoSelected();
 
-            mTabModelSelector.addObserver(new EmptyTabModelSelectorObserver() {
+            mTabModelSelectorObserver = new EmptyTabModelSelectorObserver() {
                 @Override
                 public void onTabModelSelected(TabModel newModel, TabModel oldModel) {
                     // TODO(crbug.com/982018): Optimize to not listen for selected Tab model change
                     // when overview is not shown.
                     updateIncognitoMode(newModel.isIncognito());
                 }
-            });
+            };
             mPropertyModel.set(IS_INCOGNITO, mIsIncognito);
 
             if (mSurfaceMode == SurfaceMode.TWO_PANES) {
@@ -293,6 +296,9 @@ class StartSurfaceMediator
                                 mNightModeStateProvider.isInNightMode()));
             }
 
+            updateIncognitoMode(mTabModelSelector.isIncognitoSelected());
+            mTabModelSelector.addObserver(mTabModelSelectorObserver);
+
             mPropertyModel.set(IS_SHOWING_OVERVIEW, true);
             mFakeboxDelegate.addUrlFocusChangeListener(mUrlFocusChangeListener);
         }
@@ -361,6 +367,9 @@ class StartSurfaceMediator
             if (mNormalTabModelObserver != null) {
                 mNormalTabModel.removeObserver(mNormalTabModelObserver);
             }
+            if (mTabModelSelectorObserver != null) {
+                mTabModelSelector.removeObserver(mTabModelSelectorObserver);
+            }
         }
         for (StartSurface.OverviewModeObserver observer : mObservers) {
             observer.startedHiding();

chrome/android/features/start_surface/internal/junit/src/org/chromium/chrome/features/start_surface/StartSurfaceMediatorUnitTest.java

@@ -131,7 +131,6 @@ public class StartSurfaceMediatorUnitTest {
         doReturn(true).when(mLocationBarVoiceRecognitionHandler).isVoiceSearchEnabled();
 
         StartSurfaceMediator mediator = createStartSurfaceMediator(SurfaceMode.TASKS_ONLY);
-        verify(mTabModelSelector).addObserver(mTabModelSelectorObserverCaptor.capture());
         verify(mMainTabGridController)
                 .addOverviewModeObserver(mOverviewModeObserverCaptor.capture());
         assertThat(mPropertyModel.get(IS_INCOGNITO), equalTo(false));
@@ -249,6 +248,24 @@ public class StartSurfaceMediatorUnitTest {
         verify(mNormalTabModel).removeObserver(mTabModelObserverCaptor.capture());
     }
 
+    @Test
+    public void addAndRemoveTabModelSelectorObserverWithOverview() {
+        doReturn(false).when(mTabModelSelector).isIncognitoSelected();
+        doReturn(mLocationBarVoiceRecognitionHandler)
+                .when(mFakeBoxDelegate)
+                .getLocationBarVoiceRecognitionHandler();
+        doReturn(true).when(mLocationBarVoiceRecognitionHandler).isVoiceSearchEnabled();
+
+        StartSurfaceMediator mediator = createStartSurfaceMediator(SurfaceMode.SINGLE_PANE);
+        verify(mTabModelSelector, never()).addObserver(mTabModelSelectorObserverCaptor.capture());
+
+        mediator.showOverview(false);
+        verify(mTabModelSelector).addObserver(mTabModelSelectorObserverCaptor.capture());
+
+        mediator.startedHiding();
+        verify(mTabModelSelector).removeObserver(mTabModelSelectorObserverCaptor.capture());
+    }
+
     private StartSurfaceMediator createStartSurfaceMediator(@SurfaceMode int mode) {
         return new StartSurfaceMediator(mMainTabGridController, mTabModelSelector,
                 mode == SurfaceMode.NO_START_SURFACE ? null : mPropertyModel,