[Instant Start] Fix bug in GridTabSwitcher initialization (3)

Since GridTabSwitcher has an instance of TabGridDialog, having instant
start on means that TabGridDialog can also be constructed before native.
Similar to http://crrev.com/c/2328038, this CL moves things in
TabGridDialog that should happen after native is ready to appropriate
places.

Bug: 1111391
Change-Id: I7c4e96a715b5867aa62fdd30d9e7dc2a8436d306
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2329154
Commit-Queue: Yue Zhang <yuezhanggg@chromium.org>
Reviewed-by: Wei-Yin Chen (陳威尹) <wychen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#795656}

chrome/android/features/tab_ui/java/src/org/chromium/chrome/browser/tasks/tab_management/TabGridDialogMediator.java

@@ -169,7 +169,6 @@ public class TabGridDialogMediator {
                 updateGridTabSwitcher();
             }
         };
-        mTabModelSelector.getTabModelFilterProvider().addTabModelFilterObserver(mTabModelObserver);
 
         mTabModelSelectorObserver = new EmptyTabModelSelectorObserver() {
             @Override
@@ -221,6 +220,7 @@ public class TabGridDialogMediator {
             TabGroupTitleEditor tabGroupTitleEditor) {
         mTabSelectionEditorController = tabSelectionEditorController;
         mTabGroupTitleEditor = tabGroupTitleEditor;
+        mTabModelSelector.getTabModelFilterProvider().addTabModelFilterObserver(mTabModelObserver);
 
         assert mTabModelSelector.getTabModelFilterProvider().getCurrentTabModelFilter()
                         instanceof TabGroupModelFilter;

chrome/android/features/tab_ui/javatests/src/org/chromium/chrome/browser/tasks/tab_management/TabGridDialogTest.java

@@ -710,6 +710,24 @@ public class TabGridDialogTest {
         mRenderTestRule.render(dialogView, "5_tabs_select_last");
     }
 
+    @Test
+    @MediumTest
+    @Features.EnableFeatures({ChromeFeatureList.INSTANT_START})
+    public void testSetup_WithInstantStart() {
+        final ChromeTabbedActivity cta = mActivityTestRule.getActivity();
+        prepareTabsWithThumbnail(mActivityTestRule, 2, 0, "about:blank");
+        enterTabSwitcher(cta);
+        verifyTabSwitcherCardCount(cta, 2);
+        mergeAllNormalTabsToAGroup(cta);
+        verifyTabSwitcherCardCount(cta, 1);
+        openDialogFromTabSwitcherAndVerify(cta, 2, null);
+
+        // Verify TabModelObserver is correctly setup by checking if tab grid dialog changes with
+        // tab closure.
+        closeFirstTabInDialog();
+        verifyShowingDialog(cta, 1, null);
+    }
+
     private void openDialogFromTabSwitcherAndVerify(
             ChromeTabbedActivity cta, int tabCount, String customizedTitle) {
         clickFirstCardFromTabSwitcher(cta);

chrome/android/features/tab_ui/junit/src/org/chromium/chrome/browser/tasks/tab_management/TabGridDialogMediatorUnitTest.java

@@ -193,7 +193,11 @@ public class TabGridDialogMediatorUnitTest {
         mMediator = new TabGridDialogMediator(mContext, mDialogController, mModel,
                 mTabModelSelector, mTabCreatorManager, mTabSwitcherResetHandler,
                 mAnimationSourceViewProvider, mShareDelegateSupplier, "");
+
+        // TabModelObserver is registered when native is ready.
+        assertThat(mTabModelObserverCaptor.getAllValues().isEmpty(), equalTo(true));
         mMediator.initWithNative(mTabSelectionEditorController, mTabGroupTitleEditor);
+        assertThat(mTabModelObserverCaptor.getAllValues().isEmpty(), equalTo(false));
     }
 
     @Test