Add null check for TabGridDialogResetHandler in GTS

https://crrev.com/c/1722779 This CL uses TabGridDialogResetHandler to
cancel dialog animation when tab model selection changes. However, the
reset handler can be null when #TabGroupUiImprovement flag is not
enabled. This CL fixes this issue.

Bug: 988362
Change-Id: Ic5f98ea97778617864f0e92c221a51739837d406
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1722208Reviewed-by: Wei-Yin Chen (陳威尹) <wychen@chromium.org>
Commit-Queue: Yue Zhang <yuezhanggg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#681929}

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

@@ -174,8 +174,10 @@ class GridTabSwitcherMediator implements GridTabSwitcher.GridController,
                         mTabModelSelector.getTabModelFilterProvider().getCurrentTabModelFilter();
                 mResetHandler.resetWithTabList(currentTabModelFilter, false);
                 mContainerViewModel.set(IS_INCOGNITO, currentTabModelFilter.isIncognito());
+                if (mTabGridDialogResetHandler != null) {
                     mTabGridDialogResetHandler.hideDialog(false);
                 }
+            }
         };
         mTabModelSelector.addObserver(mTabModelSelectorObserver);
 

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

@@ -182,7 +182,6 @@ public class GridTabSwitcherMediatorUnitTest {
                 mFullscreenManager, mCompositorViewHolder, null);
         mMediator.addOverviewModeObserver(mOverviewModeObserver);
         mMediator.setOnTabSelectingListener(mLayout::onTabSelecting);
-        mMediator.setTabGridDialogResetHandler(mTabGridDialogResetHandler);
     }
 
     @After
@@ -264,6 +263,7 @@ public class GridTabSwitcherMediatorUnitTest {
     @Test
     public void hidesWithAnimation() {
         initAndAssertAllProperties();
+        mMediator.setTabGridDialogResetHandler(mTabGridDialogResetHandler);
         mMediator.showOverview(true);
 
         assertThat(
@@ -282,6 +282,7 @@ public class GridTabSwitcherMediatorUnitTest {
     @Test
     public void hidesWithoutAnimation() {
         initAndAssertAllProperties();
+        mMediator.setTabGridDialogResetHandler(mTabGridDialogResetHandler);
         mMediator.showOverview(true);
 
         assertThat(
@@ -344,8 +345,10 @@ public class GridTabSwitcherMediatorUnitTest {
     }
 
     @Test
-    public void resetsAfterNewTabModelSelected() {
+    public void resetsAfterNewTabModelSelected_DialogEnabled() {
         initAndAssertAllProperties();
+        // Setup dialog reset handler. Default setup is that dialog handler is null.
+        mMediator.setTabGridDialogResetHandler(mTabGridDialogResetHandler);
 
         doReturn(true).when(mTabModelFilter).isIncognito();
         mTabModelSelectorObserverCaptor.getValue().onTabModelSelected(mTabModel, null);
@@ -357,6 +360,20 @@ public class GridTabSwitcherMediatorUnitTest {
         assertThat(mModel.get(TabListContainerProperties.IS_VISIBLE), equalTo(false));
     }
 
+    @Test
+    public void resetsAfterNewTabModelSelected_DialogNotEnabled() {
+        initAndAssertAllProperties();
+
+        doReturn(true).when(mTabModelFilter).isIncognito();
+        mTabModelSelectorObserverCaptor.getValue().onTabModelSelected(mTabModel, null);
+        verify(mResetHandler).resetWithTabList(eq(mTabModelFilter), eq(false));
+        verify(mTabGridDialogResetHandler, never()).hideDialog(eq(false));
+        assertThat(mModel.get(TabListContainerProperties.IS_INCOGNITO), equalTo(true));
+
+        // Switching TabModels by itself shouldn't cause visibility changes.
+        assertThat(mModel.get(TabListContainerProperties.IS_VISIBLE), equalTo(false));
+    }
+
     @Test
     public void updatesMarginWithBottomBarChanges() {
         initAndAssertAllProperties();