Reland "Make tab strip auto scroll to position of the selected tab"

This reverts commit e3a03f83.

Reason for revert: Try to fix the compile failure.

Original change's description:
> Revert "Make tab strip auto scroll to position of the selected tab"
> 
> This reverts commit 7767aa96.
> 
> Reason for revert: suspect causing compile failure on android-archive-rel
> 
> Sample build: https://ci.chromium.org/p/chromium/builders/ci/android-archive-rel/9648
> 
> Sample log: https://logs.chromium.org/logs/chromium/buildbucket/cr-buildbucket.appspot.com/8887341380366474896/+/steps/compile/0/stdout?format=raw
> ----
> ../../chrome/android/features/tab_ui/javatests/src/org/chromium/chrome/browser/tasks/tab_management/TabGroupUiTest.java:70: error: cannot find symbol
>         CachedFeatureFlags.setGridTabSwitcherEnabledForTesting(true);
>                           ^
>   symbol:   method setGridTabSwitcherEnabledForTesting(boolean)
>   location: class CachedFeatureFlags
> ../../chrome/android/features/tab_ui/javatests/src/org/chromium/chrome/browser/tasks/tab_management/TabGroupUiTest.java:71: error: cannot find symbol
>         CachedFeatureFlags.setTabGroupsAndroidEnabledForTesting(true);
>                           ^
>   symbol:   method setTabGroupsAndroidEnabledForTesting(boolean)
>   location: class CachedFeatureFlags
> ../../chrome/android/features/tab_ui/javatests/src/org/chromium/chrome/browser/tasks/tab_management/TabGroupUiTest.java:83: error: cannot find symbol
>         CachedFeatureFlags.setGridTabSwitcherEnabledForTesting(null);
>                           ^
>   symbol:   method setGridTabSwitcherEnabledForTesting(<null>)
>   location: class CachedFeatureFlags
> ../../chrome/android/features/tab_ui/javatests/src/org/chromium/chrome/browser/tasks/tab_management/TabGroupUiTest.java:84: error: cannot find symbol
>         CachedFeatureFlags.setTabGroupsAndroidEnabledForTesting(null);
>                           ^
>   symbol:   method setTabGroupsAndroidEnabledForTesting(<null>)
>   location: class CachedFeatureFlags
> 4 errors
> ----
> 
> Original change's description:
> > Make tab strip auto scroll to position of the selected tab
> > 
> > Currently, when a tab in group is selected or a new tab is created
> > within group, the tab strip doesn't scroll to the position of the
> > currently selected tab. This could lead to a state where user needs to
> > scroll by themselves to find their selected tab in strip. This CL fixes
> > this issue by making following changes:
> >   * Always scroll the strip to the last position when new tab is added
> >     in group.
> >   * When selected a tab in group (through tab grid dialog etc), try to
> >     scroll to a state where the selected tab is in the middle of the
> >     strip, if possible,
> > 
> > Bug: 1054079
> > Change-Id: Ic6921225d744a7b5df1853aa78e14a8f9249f2c8
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2068888
> > Commit-Queue: Yue Zhang <yuezhanggg@chromium.org>
> > Reviewed-by: Wei-Yin Chen (陳威尹) <wychen@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#744892}
> 
> TBR=yusufo@chromium.org,wychen@chromium.org,yuezhanggg@chromium.org
> 
> Change-Id: I8db970a5e6c2338ce19c8870964b96c48e66eb44
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Bug: 1054079
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2076219
> Reviewed-by: Takashi Sakamoto <tasak@google.com>
> Commit-Queue: Takashi Sakamoto <tasak@google.com>
> Cr-Commit-Position: refs/heads/master@{#744908}

TBR=tasak@google.com,yusufo@chromium.org,wychen@chromium.org,yuezhanggg@chromium.org

Change-Id: If473ca1321615dd4d2972287274f53be6e0bb574
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: 1054079
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2078415
Commit-Queue: Yue Zhang <yuezhanggg@chromium.org>
Reviewed-by: Yue Zhang <yuezhanggg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#745086}

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

@@ -44,8 +44,9 @@ public class TabGroupUiCoordinator implements TabGroupUiMediator.ResetHandler, T
     private final Context mContext;
     private final PropertyModel mModel;
     private final ThemeColorProvider mThemeColorProvider;
-    private final PropertyModelChangeProcessor mModelChangeProcessor;
+    private final TabGroupUiToolbarView mToolbarView;
     private final ViewGroup mTabListContainerView;
+    private PropertyModelChangeProcessor mModelChangeProcessor;
     private TabGridDialogCoordinator mTabGridDialogCoordinator;
     private TabListCoordinator mTabStripCoordinator;
     private TabGroupUiMediator mMediator;
@@ -59,13 +60,10 @@ public class TabGroupUiCoordinator implements TabGroupUiMediator.ResetHandler, T
         mContext = parentView.getContext();
         mThemeColorProvider = themeColorProvider;
         mModel = new PropertyModel(TabGroupUiProperties.ALL_KEYS);
-        TabGroupUiToolbarView toolbarView =
-                (TabGroupUiToolbarView) LayoutInflater.from(mContext).inflate(
-                        R.layout.bottom_tab_strip_toolbar, parentView, false);
-        mTabListContainerView = toolbarView.getViewContainer();
-        parentView.addView(toolbarView);
-        mModelChangeProcessor = PropertyModelChangeProcessor.create(
-                mModel, toolbarView, TabGroupUiViewBinder::bind);
+        mToolbarView = (TabGroupUiToolbarView) LayoutInflater.from(mContext).inflate(
+                R.layout.bottom_tab_strip_toolbar, parentView, false);
+        mTabListContainerView = mToolbarView.getViewContainer();
+        parentView.addView(mToolbarView);
     }
 
     /**
@@ -89,6 +87,11 @@ public class TabGroupUiCoordinator implements TabGroupUiMediator.ResetHandler, T
                 TabProperties.UiType.STRIP, null, mTabListContainerView, null, true,
                 COMPONENT_NAME);
 
+        mModelChangeProcessor = PropertyModelChangeProcessor.create(mModel,
+                new TabGroupUiViewBinder.ViewHolder(
+                        mToolbarView, mTabStripCoordinator.getContainerView()),
+                TabGroupUiViewBinder::bind);
+
         boolean isTabGroupsUiImprovementsEnabled =
                 TabUiFeatureUtilities.isTabGroupsAndroidUiImprovementsEnabled();
         // TODO(yuezhanggg): TabGridDialog should be the default mode.

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

@@ -4,6 +4,7 @@
 
 package org.chromium.chrome.browser.tasks.tab_management;
 
+import android.os.Handler;
 import android.view.View;
 
 import androidx.annotation.Nullable;
@@ -136,6 +137,10 @@ public class TabGroupUiMediator {
 
             @Override
             public void didAddTab(Tab tab, int type) {
+                if (type == TabLaunchType.FROM_CHROME_UI && mIsTabGroupUiVisible) {
+                    mModel.set(TabGroupUiProperties.INITIAL_SCROLL_INDEX,
+                            getRelatedTabsForId(tab.getId()).size() - 1);
+                }
                 if (type == TabLaunchType.FROM_CHROME_UI || type == TabLaunchType.FROM_RESTORE
                         || type == TabLaunchType.FROM_STARTUP) {
                     return;
@@ -284,6 +289,15 @@ public class TabGroupUiMediator {
                 && BottomToolbarConfiguration.isBottomToolbarEnabled();
         assert (mVisibilityController == null) == isDuetTabStripIntegrationEnabled;
         if (isDuetTabStripIntegrationEnabled) return;
+        if (mIsTabGroupUiVisible) {
+            // Post to make sure that the recyclerView already knows how many visible items it has.
+            // This is to make sure that we can scroll to a state where the selected tab is in the
+            // middle of the strip.
+            Handler handler = new Handler();
+            handler.post(()
+                                 -> mModel.set(TabGroupUiProperties.INITIAL_SCROLL_INDEX,
+                                         listOfTabs.indexOf(mTabModelSelector.getCurrentTab())));
+        }
         mVisibilityController.setBottomControlsVisible(mIsTabGroupUiVisible);
     }
 

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

@@ -28,8 +28,14 @@ class TabGroupUiProperties {
             new PropertyModel.WritableObjectPropertyKey<>();
     public static final PropertyModel.WritableIntPropertyKey LEFT_BUTTON_DRAWABLE_ID =
             new PropertyModel.WritableIntPropertyKey();
+    /**
+     * Integer, but not {@link PropertyModel.WritableIntPropertyKey} so that we can force update on
+     * the same value.
+     */
+    public static final PropertyModel.WritableObjectPropertyKey INITIAL_SCROLL_INDEX =
+            new PropertyModel.WritableObjectPropertyKey(true);
 
-    public static final PropertyKey[] ALL_KEYS =
-            new PropertyKey[] {LEFT_BUTTON_ON_CLICK_LISTENER, RIGHT_BUTTON_ON_CLICK_LISTENER,
-                    IS_MAIN_CONTENT_VISIBLE, PRIMARY_COLOR, TINT, LEFT_BUTTON_DRAWABLE_ID};
+    public static final PropertyKey[] ALL_KEYS = new PropertyKey[] {LEFT_BUTTON_ON_CLICK_LISTENER,
+            RIGHT_BUTTON_ON_CLICK_LISTENER, IS_MAIN_CONTENT_VISIBLE, PRIMARY_COLOR, TINT,
+            LEFT_BUTTON_DRAWABLE_ID, INITIAL_SCROLL_INDEX};
 }

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

@@ -4,6 +4,7 @@
 
 package org.chromium.chrome.browser.tasks.tab_management;
 
+import static org.chromium.chrome.browser.tasks.tab_management.TabGroupUiProperties.INITIAL_SCROLL_INDEX;
 import static org.chromium.chrome.browser.tasks.tab_management.TabGroupUiProperties.IS_MAIN_CONTENT_VISIBLE;
 import static org.chromium.chrome.browser.tasks.tab_management.TabGroupUiProperties.LEFT_BUTTON_DRAWABLE_ID;
 import static org.chromium.chrome.browser.tasks.tab_management.TabGroupUiProperties.LEFT_BUTTON_ON_CLICK_LISTENER;
@@ -11,6 +12,10 @@ import static org.chromium.chrome.browser.tasks.tab_management.TabGroupUiPropert
 import static org.chromium.chrome.browser.tasks.tab_management.TabGroupUiProperties.RIGHT_BUTTON_ON_CLICK_LISTENER;
 import static org.chromium.chrome.browser.tasks.tab_management.TabGroupUiProperties.TINT;
 
+import android.support.v7.widget.LinearLayoutManager;
+import android.support.v7.widget.RecyclerView;
+import android.view.View;
+
 import org.chromium.ui.modelutil.PropertyKey;
 import org.chromium.ui.modelutil.PropertyModel;
 
@@ -18,27 +23,48 @@ import org.chromium.ui.modelutil.PropertyModel;
  * ViewBinder for TabGroupUi component.
  */
 class TabGroupUiViewBinder {
+    /**
+     * ViewHolder class to get access to all {@link View}s inside the TabGroupUi.
+     */
+    public static class ViewHolder {
+        public final TabGroupUiToolbarView toolbarView;
+        public final RecyclerView contentView;
+
+        ViewHolder(TabGroupUiToolbarView toolbarView, RecyclerView contentView) {
+            this.toolbarView = toolbarView;
+            this.contentView = contentView;
+        }
+    }
     /**
      * Binds the given model to the given view, updating the payload in propertyKey.
      *
-     * @param model       The model to use.
-     * @param view        The view to use.
-     * @param propertyKey The key for the property to update for.
+     * @param model             The model to use.
+     * @param viewHolder        The {@link ViewHolder} to use.
+     * @param propertyKey       The key for the property to update for.
      */
-    public static void bind(
-            PropertyModel model, TabGroupUiToolbarView view, PropertyKey propertyKey) {
+    public static void bind(PropertyModel model, ViewHolder viewHolder, PropertyKey propertyKey) {
         if (LEFT_BUTTON_ON_CLICK_LISTENER == propertyKey) {
-            view.setLeftButtonOnClickListener(model.get(LEFT_BUTTON_ON_CLICK_LISTENER));
+            viewHolder.toolbarView.setLeftButtonOnClickListener(
+                    model.get(LEFT_BUTTON_ON_CLICK_LISTENER));
         } else if (RIGHT_BUTTON_ON_CLICK_LISTENER == propertyKey) {
-            view.setRightButtonOnClickListener(model.get(RIGHT_BUTTON_ON_CLICK_LISTENER));
+            viewHolder.toolbarView.setRightButtonOnClickListener(
+                    model.get(RIGHT_BUTTON_ON_CLICK_LISTENER));
         } else if (IS_MAIN_CONTENT_VISIBLE == propertyKey) {
-            view.setMainContentVisibility(model.get(IS_MAIN_CONTENT_VISIBLE));
+            viewHolder.toolbarView.setMainContentVisibility(model.get(IS_MAIN_CONTENT_VISIBLE));
         } else if (PRIMARY_COLOR == propertyKey) {
-            view.setPrimaryColor(model.get(PRIMARY_COLOR));
+            viewHolder.toolbarView.setPrimaryColor(model.get(PRIMARY_COLOR));
         } else if (TINT == propertyKey) {
-            view.setTint(model.get(TINT));
+            viewHolder.toolbarView.setTint(model.get(TINT));
         } else if (LEFT_BUTTON_DRAWABLE_ID == propertyKey) {
-            view.setLeftButtonDrawableId(model.get(LEFT_BUTTON_DRAWABLE_ID));
+            viewHolder.toolbarView.setLeftButtonDrawableId(model.get(LEFT_BUTTON_DRAWABLE_ID));
+        } else if (INITIAL_SCROLL_INDEX == propertyKey) {
+            int index = (Integer) model.get(INITIAL_SCROLL_INDEX);
+            LinearLayoutManager manager =
+                    (LinearLayoutManager) viewHolder.contentView.getLayoutManager();
+            int showingItemsCount =
+                    manager.findLastVisibleItemPosition() - manager.findFirstVisibleItemPosition();
+            // Try to scroll to a state where the selected tab is in the middle of the strip.
+            manager.scrollToPositionWithOffset(index - showingItemsCount / 2, 0);
         }
     }
 }

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

+// Copyright 2020 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package org.chromium.chrome.browser.tasks.tab_management;
+
+import static android.support.test.espresso.Espresso.onView;
+import static android.support.test.espresso.action.ViewActions.click;
+import static android.support.test.espresso.matcher.ViewMatchers.withId;
+import static android.support.test.espresso.matcher.ViewMatchers.withParent;
+
+import static org.hamcrest.Matchers.allOf;
+import static org.junit.Assert.assertTrue;
+
+import static org.chromium.chrome.browser.tasks.tab_management.TabUiTestHelper.clickFirstCardFromTabSwitcher;
+import static org.chromium.chrome.browser.tasks.tab_management.TabUiTestHelper.clickNthTabInDialog;
+import static org.chromium.chrome.browser.tasks.tab_management.TabUiTestHelper.createTabs;
+import static org.chromium.chrome.browser.tasks.tab_management.TabUiTestHelper.enterTabSwitcher;
+import static org.chromium.chrome.browser.tasks.tab_management.TabUiTestHelper.mergeAllNormalTabsToAGroup;
+import static org.chromium.chrome.browser.tasks.tab_management.TabUiTestHelper.verifyTabSwitcherCardCount;
+
+import android.support.test.filters.MediumTest;
+import android.support.v7.widget.RecyclerView;
+import android.view.ViewGroup;
+
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.TestRule;
+import org.junit.runner.RunWith;
+
+import org.chromium.base.test.util.CommandLineFlags;
+import org.chromium.base.test.util.Feature;
+import org.chromium.base.test.util.Restriction;
+import org.chromium.chrome.browser.ChromeSwitches;
+import org.chromium.chrome.browser.ChromeTabbedActivity;
+import org.chromium.chrome.browser.compositor.layouts.Layout;
+import org.chromium.chrome.browser.flags.CachedFeatureFlags;
+import org.chromium.chrome.features.start_surface.StartSurfaceLayout;
+import org.chromium.chrome.tab_ui.R;
+import org.chromium.chrome.test.ChromeJUnit4ClassRunner;
+import org.chromium.chrome.test.ChromeTabbedActivityTestRule;
+import org.chromium.chrome.test.util.ChromeRenderTestRule;
+import org.chromium.chrome.test.util.browser.Features;
+import org.chromium.content_public.browser.test.util.CriteriaHelper;
+import org.chromium.ui.test.util.UiRestriction;
+
+import java.io.IOException;
+
+/** End-to-end tests for TabGroupUi component. */
+@RunWith(ChromeJUnit4ClassRunner.class)
+// clang-format off
+@CommandLineFlags.Add({ChromeSwitches.DISABLE_FIRST_RUN_EXPERIENCE})
+@Restriction(UiRestriction.RESTRICTION_TYPE_PHONE)
+public class TabGroupUiTest {
+    // clang-format on
+
+    @Rule
+    public ChromeTabbedActivityTestRule mActivityTestRule = new ChromeTabbedActivityTestRule();
+
+    @Rule
+    public TestRule mProcessor = new Features.InstrumentationProcessor();
+
+    @Rule
+    public ChromeRenderTestRule mRenderTestRule = new ChromeRenderTestRule();
+
+    @Before
+    public void setUp() {
+        CachedFeatureFlags.setForTesting(ChromeFeatureList.TAB_GRID_LAYOUT_ANDROID, true);
+        CachedFeatureFlags.setForTesting(ChromeFeatureList.TAB_GROUPS_ANDROID, true);
+        mActivityTestRule.startMainActivityFromLauncher();
+        Layout layout = mActivityTestRule.getActivity().getLayoutManager().getOverviewLayout();
+        assertTrue(layout instanceof StartSurfaceLayout);
+        CriteriaHelper.pollUiThread(mActivityTestRule.getActivity()
+                                            .getTabModelSelector()
+                                            .getTabModelFilterProvider()
+                                            .getCurrentTabModelFilter()::isTabModelRestored);
+    }
+
+    @After
+    public void tearDown() {
+        CachedFeatureFlags.setForTesting(ChromeFeatureList.TAB_GRID_LAYOUT_ANDROID, null);
+        CachedFeatureFlags.setForTesting(ChromeFeatureList.TAB_GROUPS_ANDROID, null);
+    }
+
+    @Test
+    @MediumTest
+    @Feature({"RenderTest"})
+    public void testRenderStrip_Select5thTabIn10Tabs() throws InterruptedException, IOException {
+        final ChromeTabbedActivity cta = mActivityTestRule.getActivity();
+        createTabs(cta, false, 10);
+        enterTabSwitcher(cta);
+        verifyTabSwitcherCardCount(cta, 10);
+        mergeAllNormalTabsToAGroup(cta);
+        verifyTabSwitcherCardCount(cta, 1);
+
+        // Select the 5th tab in group.
+        clickFirstCardFromTabSwitcher(cta);
+        clickNthTabInDialog(cta, 4);
+
+        ViewGroup bottomToolbar = cta.findViewById(R.id.bottom_controls);
+        RecyclerView stripRecyclerView =
+                (RecyclerView) bottomToolbar.findViewById(R.id.tab_list_view);
+        mRenderTestRule.render(stripRecyclerView, "5th_tab_selected");
+    }
+
+    @Test
+    @MediumTest
+    @Feature({"RenderTest"})
+    public void testRenderStrip_Select10thTabIn10Tabs() throws InterruptedException, IOException {
+        final ChromeTabbedActivity cta = mActivityTestRule.getActivity();
+        createTabs(cta, false, 10);
+        enterTabSwitcher(cta);
+        verifyTabSwitcherCardCount(cta, 10);
+        mergeAllNormalTabsToAGroup(cta);
+        verifyTabSwitcherCardCount(cta, 1);
+
+        // Select the 10th tab in group.
+        clickFirstCardFromTabSwitcher(cta);
+        clickNthTabInDialog(cta, 9);
+
+        ViewGroup bottomToolbar = cta.findViewById(R.id.bottom_controls);
+        RecyclerView stripRecyclerView =
+                (RecyclerView) bottomToolbar.findViewById(R.id.tab_list_view);
+        mRenderTestRule.render(stripRecyclerView, "10th_tab_selected");
+    }
+
+    @Test
+    @MediumTest
+    @Feature({"RenderTest"})
+    public void testRenderStrip_AddTab() throws InterruptedException, IOException {
+        final ChromeTabbedActivity cta = mActivityTestRule.getActivity();
+        createTabs(cta, false, 10);
+        enterTabSwitcher(cta);
+        verifyTabSwitcherCardCount(cta, 10);
+        mergeAllNormalTabsToAGroup(cta);
+        verifyTabSwitcherCardCount(cta, 1);
+
+        // Select the first tab in group and add one new tab to group.
+        clickFirstCardFromTabSwitcher(cta);
+        clickNthTabInDialog(cta, 0);
+        ViewGroup bottomToolbar = cta.findViewById(R.id.bottom_controls);
+        RecyclerView stripRecyclerView =
+                (RecyclerView) bottomToolbar.findViewById(R.id.tab_list_view);
+        stripRecyclerView.setItemAnimator(null);
+        onView(allOf(withId(R.id.toolbar_right_button), withParent(withId(R.id.main_content))))
+                .perform(click());
+        mRenderTestRule.render(stripRecyclerView, "11th_tab_selected");
+    }
+}

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

@@ -16,6 +16,8 @@ import android.graphics.drawable.Drawable;
 import android.os.Build;
 import android.support.test.annotation.UiThreadTest;
 import android.support.test.filters.SmallTest;
+import android.support.v7.widget.LinearLayoutManager;
+import android.support.v7.widget.RecyclerView;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
@@ -61,9 +63,16 @@ public class TabGroupUiViewBinderTest extends DummyUiActivityTestCase {
         mRightButton = toolbarView.findViewById(R.id.toolbar_right_button);
         mContainerView = toolbarView.findViewById(R.id.toolbar_container_view);
         mMainContent = toolbarView.findViewById(R.id.main_content);
+        RecyclerView recyclerView =
+                (TabListRecyclerView) LayoutInflater.from(getActivity())
+                        .inflate(R.layout.tab_list_recycler_view_layout, parentView, false);
+        recyclerView.setLayoutManager(
+                new LinearLayoutManager(getActivity(), LinearLayoutManager.HORIZONTAL, false));
 
         mModel = new PropertyModel(TabGroupUiProperties.ALL_KEYS);
-        mMCP = PropertyModelChangeProcessor.create(mModel, toolbarView, TabGroupUiViewBinder::bind);
+        mMCP = PropertyModelChangeProcessor.create(mModel,
+                new TabGroupUiViewBinder.ViewHolder(toolbarView, recyclerView),
+                TabGroupUiViewBinder::bind);
     }
 
     @Override

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

@@ -408,6 +408,26 @@ public class TabGroupUiMediatorUnitTest {
         verifyNeverReset();
     }
 
+    @Test
+    public void tabSelection_ScrollToSelectedIndex() {
+        initAndAssertProperties(mTab1);
+        assertThat(mModel.get(TabGroupUiProperties.INITIAL_SCROLL_INDEX), equalTo(null));
+
+        // Mock that {tab2, tab3} are in the same tab group.
+        List<Tab> tabGroup = mTabGroupModelFilter.getRelatedTabList(TAB2_ID);
+        assertThat(tabGroup.size(), equalTo(2));
+
+        // Mock selecting tab 3, and the last selected tab is tab 1 which is a single tab.
+        doReturn(mTab3).when(mTabModelSelector).getCurrentTab();
+        mTabModelObserverArgumentCaptor.getValue().didSelectTab(
+                mTab3, TabSelectionType.FROM_USER, TAB1_ID);
+
+        // Strip should be showing since we are selecting a group, and it should scroll to the index
+        // of currently selected tab.
+        verifyResetStrip(true, tabGroup);
+        assertThat(mModel.get(TabGroupUiProperties.INITIAL_SCROLL_INDEX), equalTo(1));
+    }
+
     @Test
     public void tabClosure_NotLastTabInGroup() {
         initAndAssertProperties(mTab2);
@@ -500,6 +520,23 @@ public class TabGroupUiMediatorUnitTest {
         verifyResetStrip(true, mTabGroup2);
     }
 
+    @Test
+    public void tabAddition_TabGroup_ScrollToTheLast() {
+        initAndAssertProperties(mTab2);
+        assertThat(mModel.get(TabGroupUiProperties.INITIAL_SCROLL_INDEX), equalTo(0));
+
+        TabImpl newTab = prepareTab(TAB4_ID, TAB4_ID);
+        mTabGroup2.add(newTab);
+        doReturn(mTabGroup2).when(mTabGroupModelFilter).getRelatedTabList(TAB4_ID);
+
+        mTabModelObserverArgumentCaptor.getValue().didAddTab(newTab, TabLaunchType.FROM_CHROME_UI);
+
+        // Strip should be not be reset through adding tab from UI.
+        verifyNeverReset();
+        assertThat(mTabGroupModelFilter.getRelatedTabList(TAB4_ID).size(), equalTo(3));
+        assertThat(mModel.get(TabGroupUiProperties.INITIAL_SCROLL_INDEX), equalTo(2));
+    }
+
     @Test
     public void restoreCompleted_TabModelNoTab() {
         // Simulate no tab in current TabModel.

chrome/android/features/tab_ui/tab_management_java_sources.gni

@@ -40,6 +40,7 @@ tab_management_test_java_sources = [
   "//chrome/android/features/tab_ui/javatests/src/org/chromium/chrome/browser/tasks/tab_management/TabGridPanelViewBinderTest.java",
   "//chrome/android/features/tab_ui/javatests/src/org/chromium/chrome/browser/tasks/tab_management/TabGroupPopupUiTest.java",
   "//chrome/android/features/tab_ui/javatests/src/org/chromium/chrome/browser/tasks/tab_management/TabGroupPopupUiViewBinderTest.java",
+  "//chrome/android/features/tab_ui/javatests/src/org/chromium/chrome/browser/tasks/tab_management/TabGroupUiTest.java",
   "//chrome/android/features/tab_ui/javatests/src/org/chromium/chrome/browser/tasks/tab_management/TabGroupUiViewBinderTest.java",
   "//chrome/android/features/tab_ui/javatests/src/org/chromium/chrome/browser/tasks/tab_management/TabListContainerViewBinderTest.java",
   "//chrome/android/features/tab_ui/javatests/src/org/chromium/chrome/browser/tasks/tab_management/TabListViewHolderTest.java",

chrome/test/data/android/render_tests/TabGroupUiTest.10th_tab_selected.Nexus_5-19.png.sha1

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