Fix add tab misbehavior when there is no tab in dialog

Currently when user clicks to add a new tab in TabGridDialog, we try to
create a new tab which takes the last tab in this group as parent.
However, this can be problematic when all tabs are closed in this group.
This CL fixes this issue.

Bug: 987885
Change-Id: I1a6c83f9bfe8e55669ed5424cb7f096e277a91e1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1726413Reviewed-by: Wei-Yin Chen (陳威尹) <wychen@chromium.org>
Commit-Queue: Yue Zhang <yuezhanggg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#682367}

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

@@ -229,6 +229,11 @@ public class TabGridDialogMediator {
         return view -> {
             hideDialog(false);
             Tab currentTab = mTabModelSelector.getTabById(mCurrentTabId);
+            if (currentTab == null) {
+                mTabCreatorManager.getTabCreator(mTabModelSelector.isIncognitoSelected())
+                        .launchNTP();
+                return;
+            }
             List<Tab> relatedTabs = getRelatedTabs(currentTab.getId());
 
             assert relatedTabs.size() > 0;

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

@@ -9,6 +9,8 @@ import static org.hamcrest.CoreMatchers.instanceOf;
 import static org.junit.Assert.assertThat;
 import static org.mockito.ArgumentMatchers.anyBoolean;
 import static org.mockito.ArgumentMatchers.anyInt;
+import static org.mockito.ArgumentMatchers.eq;
+import static org.mockito.ArgumentMatchers.isA;
 import static org.mockito.Mockito.doNothing;
 import static org.mockito.Mockito.doReturn;
 import static org.mockito.Mockito.mock;
@@ -45,6 +47,7 @@ import org.chromium.chrome.browser.tabmodel.TabSelectionType;
 import org.chromium.chrome.browser.tasks.tab_groups.TabGroupModelFilter;
 import org.chromium.chrome.browser.widget.ScrimView;
 import org.chromium.chrome.test.util.browser.Features;
+import org.chromium.content_public.browser.LoadUrlParams;
 import org.chromium.testing.local.LocalRobolectricTestRunner;
 import org.chromium.ui.modelutil.PropertyModel;
 
@@ -177,7 +180,7 @@ public class TabGridDialogMediatorUnitTest {
     }
 
     @Test
-    public void onClickAdd() {
+    public void onClickAdd_HasCurrentTab() {
         // Mock that the animation source Rect is not null.
         mModel.set(TabGridSheetProperties.ANIMATION_SOURCE_RECT, mRect);
         mMediator.setCurrentTabIdForTest(TAB1_ID);
@@ -187,6 +190,19 @@ public class TabGridDialogMediatorUnitTest {
 
         assertThat(mModel.get(TabGridSheetProperties.ANIMATION_SOURCE_RECT), equalTo(null));
         verify(mDialogResetHandler).resetWithListOfTabs(null);
+        verify(mTabCreator)
+                .createNewTab(
+                        isA(LoadUrlParams.class), eq(TabLaunchType.FROM_CHROME_UI), eq(mTab1));
+    }
+
+    @Test
+    public void onClickAdd_NoCurrentTab() {
+        mMediator.setCurrentTabIdForTest(Tab.INVALID_TAB_ID);
+
+        View.OnClickListener listener = mModel.get(TabGridSheetProperties.ADD_CLICK_LISTENER);
+        listener.onClick(mView);
+
+        verify(mTabCreator).launchNTP();
     }
 
     @Test