Make transition animation in Grid Tab Switcher closer to spec

Updates in both Tab-to-Grid and Grid-to-Tab transition animations:
- Stops showing the tab decoration when the tab resizes
- Fade in/fade out the GTS in the background when the tab resizes
- Update interpolator for tab resizing

Updates in Tab-to-Grid transition animation:
- Duration of GTS final fading-in: 218ms -> 50ms
- Delay the fading-in of Tab Switcher top toolbar to the second half
  of the animation

Bug: 971522
Change-Id: Ifc34437cb6691b18f0e4c63439b464b637927310
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1646741
Commit-Queue: Wei-Yin Chen (陳威尹) <wychen@chromium.org>
Reviewed-by: Matthew Jones <mdjones@chromium.org>
Reviewed-by: Yusuf Ozuysal <yusufo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#667193}

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

@@ -29,6 +29,7 @@ import org.chromium.ui.resources.dynamics.ViewResourceAdapter;
  */
 class TabListRecyclerView extends RecyclerView {
     public static final long BASE_ANIMATION_DURATION_MS = 218;
+    public static final long FINAL_FADE_IN_DURATION_MS = 50;
     public static final long RESTORE_ANIMATION_DURATION_MS = 10;
     public static final int ANIMATION_STATUS_RESTORE = 0;
     public static final int ANIMATION_STATUS_ZOOM_OUT = 1;
@@ -106,11 +107,15 @@ class TabListRecyclerView extends RecyclerView {
         assert mFadeOutAnimator == null;
         mListener.startedShowing(animate);
 
+        long duration = ChromeFeatureList.isEnabled(ChromeFeatureList.TAB_TO_GTS_ANIMATION)
+                ? FINAL_FADE_IN_DURATION_MS
+                : BASE_ANIMATION_DURATION_MS;
+
         setAlpha(0);
         setVisibility(View.VISIBLE);
         mFadeInAnimator = ObjectAnimator.ofFloat(this, View.ALPHA, 1);
         mFadeInAnimator.setInterpolator(BakedBezierInterpolator.FADE_IN_CURVE);
-        mFadeInAnimator.setDuration(BASE_ANIMATION_DURATION_MS);
+        mFadeInAnimator.setDuration(duration);
         mFadeInAnimator.start();
         mFadeInAnimator.addListener(new AnimatorListenerAdapter() {
             @Override

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

@@ -17,17 +17,23 @@ import android.view.View;
 import android.widget.FrameLayout;
 
 import org.junit.BeforeClass;
+import org.junit.Rule;
 import org.junit.Test;
+import org.junit.rules.TestRule;
 import org.junit.runner.RunWith;
 
 import org.chromium.base.ApiCompatibilityUtils;
+import org.chromium.base.CommandLine;
 import org.chromium.base.ContextUtils;
 import org.chromium.base.test.util.CallbackHelper;
 import org.chromium.base.test.util.DisabledTest;
+import org.chromium.chrome.browser.ChromeFeatureList;
+import org.chromium.chrome.browser.util.FeatureUtilities;
 import org.chromium.chrome.tab_ui.R;
 import org.chromium.chrome.test.ChromeJUnit4ClassRunner;
 import org.chromium.chrome.test.ui.DummyUiActivity;
 import org.chromium.chrome.test.ui.DummyUiActivityTestCase;
+import org.chromium.chrome.test.util.browser.Features;
 import org.chromium.content_public.browser.test.util.Criteria;
 import org.chromium.content_public.browser.test.util.CriteriaHelper;
 import org.chromium.content_public.browser.test.util.TestThreadUtils;
@@ -39,6 +45,14 @@ import org.chromium.ui.modelutil.PropertyModelChangeProcessor;
  */
 @RunWith(ChromeJUnit4ClassRunner.class)
 public class TabGridContainerViewBinderTest extends DummyUiActivityTestCase {
+    /**
+     * DummyUiActivityTestCase also needs {@link ChromeFeatureList}'s
+     * internal test-only feature map, not the {@link CommandLine} provided by
+     * {@link Features.InstrumentationProcessor}.
+     */
+    @Rule
+    public TestRule mProcessor = new Features.JUnitProcessor();
+
     private static final int CONTAINER_HEIGHT = 56;
     private TabGridContainerViewBinder mTabGridContainerViewHolder;
     private PropertyModel mContainerModel;
@@ -83,6 +97,7 @@ public class TabGridContainerViewBinderTest extends DummyUiActivityTestCase {
     @Override
     public void setUpTest() throws Exception {
         super.setUpTest();
+        FeatureUtilities.setGridTabSwitcherEnabledForTesting(true);
 
         TestThreadUtils.runOnUiThreadBlocking(
                 () -> { mRecyclerView = getActivity().findViewById(R.id.tab_list_view); });
@@ -100,6 +115,7 @@ public class TabGridContainerViewBinderTest extends DummyUiActivityTestCase {
 
     @Test
     @MediumTest
+    @Features.EnableFeatures(ChromeFeatureList.TAB_TO_GTS_ANIMATION)
     @DisabledTest
     // Failed multiple times on Android CFI https://crbug.com/954145
     public void testShowWithAnimation() throws Exception {
@@ -129,6 +145,7 @@ public class TabGridContainerViewBinderTest extends DummyUiActivityTestCase {
     @Test
     @MediumTest
     @UiThreadTest
+    @Features.EnableFeatures(ChromeFeatureList.TAB_TO_GTS_ANIMATION)
     public void testShowWithoutAnimation() throws Exception {
         mContainerModel.set(
                 TabListContainerProperties.VISIBILITY_LISTENER, mMockVisibilityListener);
@@ -145,6 +162,7 @@ public class TabGridContainerViewBinderTest extends DummyUiActivityTestCase {
 
     @Test
     @MediumTest
+    @Features.EnableFeatures(ChromeFeatureList.TAB_TO_GTS_ANIMATION)
     public void testHidesWithAnimation() throws Exception {
         TestThreadUtils.runOnUiThreadBlocking(() -> {
             mContainerModel.set(
@@ -182,6 +200,7 @@ public class TabGridContainerViewBinderTest extends DummyUiActivityTestCase {
     @Test
     @MediumTest
     @UiThreadTest
+    @Features.EnableFeatures(ChromeFeatureList.TAB_TO_GTS_ANIMATION)
     public void testHidesWithoutAnimation() throws Exception {
         mContainerModel.set(
                 TabListContainerProperties.VISIBILITY_LISTENER, mMockVisibilityListener);

chrome/android/java/src/org/chromium/chrome/browser/compositor/animation/CompositorAnimator.java

@@ -13,7 +13,9 @@ import android.provider.Settings;
 import android.support.annotation.IntDef;
 import android.support.annotation.NonNull;
 import android.support.annotation.Nullable;
+import android.support.v4.view.animation.FastOutLinearInInterpolator;
 import android.support.v4.view.animation.FastOutSlowInInterpolator;
+import android.support.v4.view.animation.LinearOutSlowInInterpolator;
 import android.view.animation.AccelerateInterpolator;
 import android.view.animation.DecelerateInterpolator;
 import android.view.animation.LinearInterpolator;
@@ -114,6 +116,10 @@ public class CompositorAnimator extends Animator {
             new DecelerateInterpolator();
     public static final FastOutSlowInInterpolator FAST_OUT_SLOW_IN_INTERPOLATOR =
             new FastOutSlowInInterpolator();
+    public static final LinearOutSlowInInterpolator LINEAR_OUT_SLOW_IN_INTERPOLATOR =
+            new LinearOutSlowInInterpolator();
+    public static final FastOutLinearInInterpolator FAST_OUT_LINEAR_IN_INTERPOLATOR =
+            new FastOutLinearInInterpolator();
     public static final LinearInterpolator LINEAR_INTERPOLATOR = new LinearInterpolator();
 
     /**
@@ -157,6 +163,29 @@ public class CompositorAnimator extends Animator {
         return animator;
     }
 
+    /**
+     * A utility for creating a basic animator.
+     * @param handler The {@link CompositorAnimationHandler} responsible for running the animation.
+     * @param target The object to modify.
+     * @param property The property of the object to modify.
+     * @param startValue The {@link Supplier} of the starting animation value.
+     * @param endValue The {@link Supplier} of the end animation value.
+     * @param durationMs The duration of the animation in ms.
+     * @param interpolator The time interpolator for the animation.
+     * @return A {@link CompositorAnimator} for the property.
+     */
+    public static <T> CompositorAnimator ofFloatProperty(CompositorAnimationHandler handler,
+            final T target, final FloatProperty<T> property, Supplier<Float> startValue,
+            Supplier<Float> endValue, long durationMs, TimeInterpolator interpolator) {
+        CompositorAnimator animator = new CompositorAnimator(handler);
+        animator.setValues(startValue, endValue);
+        animator.setDuration(durationMs);
+        animator.addUpdateListener(
+                (CompositorAnimator a) -> property.setValue(target, a.getAnimatedValue()));
+        animator.setInterpolator(interpolator);
+        return animator;
+    }
+
     /**
      * A utility for creating a basic animator.
      * @param handler The {@link CompositorAnimationHandler} responsible for running the animation.
@@ -187,12 +216,8 @@ public class CompositorAnimator extends Animator {
     public static <T> CompositorAnimator ofFloatProperty(CompositorAnimationHandler handler,
             final T target, final FloatProperty<T> property, Supplier<Float> startValue,
             Supplier<Float> endValue, long durationMs) {
-        CompositorAnimator animator = new CompositorAnimator(handler);
-        animator.setValues(startValue, endValue);
-        animator.setDuration(durationMs);
-        animator.addUpdateListener(
-                (CompositorAnimator a) -> property.setValue(target, a.getAnimatedValue()));
-        return animator;
+        return ofFloatProperty(handler, target, property, startValue, endValue, durationMs,
+                DECELERATE_INTERPOLATOR);
     }
 
     /** An interface for listening for frames of an animation. */

chrome/android/java/src/org/chromium/chrome/browser/compositor/layouts/ToolbarSwipeLayout.java

@@ -403,7 +403,7 @@ public class ToolbarSwipeLayout extends Layout {
         // contentViewport is intentionally passed for both parameters below.
         mSceneLayer.pushLayers(getContext(), contentViewport, contentViewport, this,
                 layerTitleCache, tabContentManager, resourceManager, fullscreenManager,
-                SceneLayer.INVALID_RESOURCE_ID);
+                SceneLayer.INVALID_RESOURCE_ID, 0);
     }
 
     /**

chrome/android/java/src/org/chromium/chrome/browser/compositor/layouts/phone/SimpleAnimationLayout.java

@@ -457,6 +457,6 @@ public class SimpleAnimationLayout extends Layout {
         // The content viewport is intentionally sent as both params below.
         mSceneLayer.pushLayers(getContext(), contentViewport, contentViewport, this,
                 layerTitleCache, tabContentManager, resourceManager, fullscreenManager,
-                SceneLayer.INVALID_RESOURCE_ID);
+                SceneLayer.INVALID_RESOURCE_ID, 0);
     }
 }

chrome/android/java/src/org/chromium/chrome/browser/compositor/layouts/phone/StackLayoutBase.java

@@ -1621,7 +1621,7 @@ public abstract class StackLayoutBase extends Layout {
 
         mSceneLayer.pushLayers(getContext(), viewport, contentViewport, this, layerTitleCache,
                 tabContentManager, resourceManager, fullscreenManager,
-                SceneLayer.INVALID_RESOURCE_ID);
+                SceneLayer.INVALID_RESOURCE_ID, 0);
     }
 
     /**

chrome/android/java/src/org/chromium/chrome/browser/compositor/scene_layer/TabListSceneLayer.java

@@ -56,7 +56,7 @@ public class TabListSceneLayer extends SceneLayer {
     public void pushLayers(Context context, RectF viewport, RectF contentViewport, Layout layout,
             LayerTitleCache layerTitleCache, TabContentManager tabContentManager,
             ResourceManager resourceManager, ChromeFullscreenManager fullscreenManager,
-            int backgroundResourceId) {
+            int backgroundResourceId, float backgroundAlpha) {
         if (mNativePtr == 0) return;
 
         Resources res = context.getResources();
@@ -72,7 +72,7 @@ public class TabListSceneLayer extends SceneLayer {
                 viewport.height(), layerTitleCache, tabContentManager, resourceManager);
 
         if (backgroundResourceId != INVALID_RESOURCE_ID) {
-            nativePutBackgroundLayer(mNativePtr, backgroundResourceId);
+            nativePutBackgroundLayer(mNativePtr, backgroundResourceId, backgroundAlpha);
         }
 
         boolean isHTSEnabled =
@@ -207,5 +207,6 @@ public class TabListSceneLayer extends SceneLayer {
             float toolbarTextBoxAlpha, float toolbarAlpha, float toolbarYOffset,
             float sideBorderScale, boolean insetVerticalBorder);
 
-    private native void nativePutBackgroundLayer(long nativeTabListSceneLayer, int resourceId);
+    private native void nativePutBackgroundLayer(
+            long nativeTabListSceneLayer, int resourceId, float alpha);
 }

chrome/android/java/src/org/chromium/chrome/browser/toolbar/top/TabSwitcherModeTTPhone.java

@@ -146,10 +146,18 @@ public class TabSwitcherModeTTPhone extends OptimizedFrameLayout
         // TODO(twellington): Handle interrupted animations to avoid jumps to 1.0 or 0.f.
         setAlpha(inTabSwitcherMode ? 0.0f : 1.0f);
 
+        boolean showZoomingAnimation = FeatureUtilities.isGridTabSwitcherEnabled()
+                && ChromeFeatureList.isEnabled(ChromeFeatureList.TAB_TO_GTS_ANIMATION);
+        long duration = showZoomingAnimation
+                ? TopToolbarCoordinator.TAB_SWITCHER_MODE_GTS_ANIMATION_DURATION_MS
+                : TopToolbarCoordinator.TAB_SWITCHER_MODE_NORMAL_ANIMATION_DURATION_MS;
+
         mVisiblityAnimator =
                 ObjectAnimator.ofFloat(this, View.ALPHA, inTabSwitcherMode ? 1.0f : 0.0f);
-        mVisiblityAnimator.setDuration(
-                TopToolbarCoordinator.TAB_SWITCHER_MODE_NORMAL_ANIMATION_DURATION_MS);
+        mVisiblityAnimator.setDuration(duration);
+        if (showZoomingAnimation && inTabSwitcherMode) {
+            mVisiblityAnimator.setStartDelay(duration);
+        }
         mVisiblityAnimator.setInterpolator(new LinearInterpolator());
 
         // TODO(https://crbug.com/914868): Use consistent logic here for setting clickable/enabled

chrome/android/java/src/org/chromium/chrome/browser/toolbar/top/TopToolbarCoordinator.java

@@ -35,6 +35,7 @@ import org.chromium.chrome.browser.widget.ToolbarProgressBar;
  */
 public class TopToolbarCoordinator implements Toolbar {
     static final int TAB_SWITCHER_MODE_NORMAL_ANIMATION_DURATION_MS = 200;
+    static final int TAB_SWITCHER_MODE_GTS_ANIMATION_DURATION_MS = 150;
 
     /**
      * Observes toolbar URL expansion percentage change.

chrome/android/java/src/org/chromium/chrome/browser/widget/GridTabSwitcherLayout.java

@@ -4,6 +4,8 @@
 
 package org.chromium.chrome.browser.widget;
 
+import static org.chromium.chrome.browser.compositor.animation.CompositorAnimator.FAST_OUT_SLOW_IN_INTERPOLATOR;
+
 import android.animation.Animator;
 import android.animation.AnimatorListenerAdapter;
 import android.animation.AnimatorSet;
@@ -32,7 +34,6 @@ import org.chromium.chrome.browser.compositor.scene_layer.TabListSceneLayer;
 import org.chromium.chrome.browser.fullscreen.ChromeFullscreenManager;
 import org.chromium.chrome.browser.tab.Tab;
 import org.chromium.chrome.browser.tasks.tab_management.GridTabSwitcher;
-import org.chromium.ui.interpolators.BakedBezierInterpolator;
 import org.chromium.ui.resources.ResourceManager;
 import org.chromium.ui.widget.Toast;
 
@@ -50,6 +51,7 @@ public class GridTabSwitcherLayout
     // Duration of the transition animation
     @VisibleForTesting
     static final long ZOOMING_DURATION = 300;
+    private static final int BACKGROUND_FADING_DURATION_MS = 150;
 
     /** Field trial parameter for whether skipping slow zooming animation */
     private static final String SKIP_SLOW_ZOOMING_PARAM = "skip-slow-zooming";
@@ -64,6 +66,8 @@ public class GridTabSwitcherLayout
     // To force Toolbar finishes its animation when this Layout finished hiding.
     private final LayoutTab mDummyLayoutTab;
 
+    private float mBackgroundAlpha;
+
     private int mFrameCount;
     private long mStartTime;
     private long mLastFrameTime;
@@ -204,6 +208,7 @@ public class GridTabSwitcherLayout
     private void shrinkTab(Supplier<Rect> target) {
         LayoutTab sourceLayoutTab = createLayoutTab(mTabModelSelector.getCurrentTabId(),
                 mTabModelSelector.isIncognitoSelected(), NO_CLOSE_BUTTON, NEED_TITLE);
+        sourceLayoutTab.setDecorationAlpha(0);
 
         mLayoutTabs = new LayoutTab[] {sourceLayoutTab};
 
@@ -216,18 +221,26 @@ public class GridTabSwitcherLayout
         animationList.add(CompositorAnimator.ofFloatProperty(
                 handler, sourceLayoutTab, LayoutTab.SCALE, () -> 1f, () -> {
                     return target.get().width() / (getWidth() * mDpToPx);
-                }, ZOOMING_DURATION));
-        animationList.add(CompositorAnimator.ofFloatProperty(handler, sourceLayoutTab, LayoutTab.X,
-                () -> 0f, () -> { return target.get().left / mDpToPx; }, ZOOMING_DURATION));
-        animationList.add(CompositorAnimator.ofFloatProperty(handler, sourceLayoutTab, LayoutTab.Y,
-                () -> 0f, () -> { return target.get().top / mDpToPx; }, ZOOMING_DURATION));
+                }, ZOOMING_DURATION, FAST_OUT_SLOW_IN_INTERPOLATOR));
+        animationList.add(CompositorAnimator.ofFloatProperty(
+                handler, sourceLayoutTab, LayoutTab.X, () -> 0f, () -> {
+                    return target.get().left / mDpToPx;
+                }, ZOOMING_DURATION, FAST_OUT_SLOW_IN_INTERPOLATOR));
         animationList.add(CompositorAnimator.ofFloatProperty(
-                handler, sourceLayoutTab, LayoutTab.DECORATION_ALPHA, 1f, 0f, ZOOMING_DURATION));
+                handler, sourceLayoutTab, LayoutTab.Y, () -> 0f, () -> {
+                    return target.get().top / mDpToPx;
+                }, ZOOMING_DURATION, FAST_OUT_SLOW_IN_INTERPOLATOR));
         // TODO(crbug.com/964406): when shrinking to the bottom row, bottom of the tab goes up and
         // down, making the "create group" visible for a while.
         animationList.add(CompositorAnimator.ofFloatProperty(handler, sourceLayoutTab,
                 LayoutTab.MAX_CONTENT_HEIGHT, sourceLayoutTab.getUnclampedOriginalContentHeight(),
-                getWidth(), ZOOMING_DURATION, BakedBezierInterpolator.FADE_OUT_CURVE));
+                getWidth(), ZOOMING_DURATION, FAST_OUT_SLOW_IN_INTERPOLATOR));
+
+        CompositorAnimator backgroundAlpha =
+                CompositorAnimator.ofFloat(handler, 0f, 1f, BACKGROUND_FADING_DURATION_MS,
+                        animator -> mBackgroundAlpha = animator.getAnimatedValue());
+        backgroundAlpha.setInterpolator(CompositorAnimator.FAST_OUT_LINEAR_IN_INTERPOLATOR);
+        animationList.add(backgroundAlpha);
 
         mTabToSwitcherAnimation = new AnimatorSet();
         mTabToSwitcherAnimation.playTogether(animationList);
@@ -255,6 +268,7 @@ public class GridTabSwitcherLayout
     private void expandTab(Rect source) {
         LayoutTab sourceLayoutTab = createLayoutTab(mTabModelSelector.getCurrentTabId(),
                 mTabModelSelector.isIncognitoSelected(), NO_CLOSE_BUTTON, NEED_TITLE);
+        sourceLayoutTab.setDecorationAlpha(0);
 
         mLayoutTabs = new LayoutTab[] {sourceLayoutTab};
 
@@ -265,19 +279,24 @@ public class GridTabSwitcherLayout
 
         // Zoom in the source tab
         animationList.add(CompositorAnimator.ofFloatProperty(handler, sourceLayoutTab,
-                LayoutTab.SCALE, source.width() / (getWidth() * mDpToPx), 1, ZOOMING_DURATION));
+                LayoutTab.SCALE, source.width() / (getWidth() * mDpToPx), 1, ZOOMING_DURATION,
+                FAST_OUT_SLOW_IN_INTERPOLATOR));
         animationList.add(CompositorAnimator.ofFloatProperty(handler, sourceLayoutTab, LayoutTab.X,
-                source.left / mDpToPx, 0f, ZOOMING_DURATION));
-        animationList.add(CompositorAnimator.ofFloatProperty(
-                handler, sourceLayoutTab, LayoutTab.Y, source.top / mDpToPx, 0f, ZOOMING_DURATION));
-        animationList.add(CompositorAnimator.ofFloatProperty(
-                handler, sourceLayoutTab, LayoutTab.DECORATION_ALPHA, 0f, 1f, ZOOMING_DURATION));
+                source.left / mDpToPx, 0f, ZOOMING_DURATION, FAST_OUT_SLOW_IN_INTERPOLATOR));
+        animationList.add(CompositorAnimator.ofFloatProperty(handler, sourceLayoutTab, LayoutTab.Y,
+                source.top / mDpToPx, 0f, ZOOMING_DURATION, FAST_OUT_SLOW_IN_INTERPOLATOR));
         // TODO(crbug.com/964406): when shrinking to the bottom row, bottom of the tab goes up and
         // down, making the "create group" visible for a while.
         animationList.add(CompositorAnimator.ofFloatProperty(handler, sourceLayoutTab,
                 LayoutTab.MAX_CONTENT_HEIGHT, getWidth(),
                 sourceLayoutTab.getUnclampedOriginalContentHeight(), ZOOMING_DURATION,
-                BakedBezierInterpolator.FADE_IN_CURVE));
+                FAST_OUT_SLOW_IN_INTERPOLATOR));
+
+        CompositorAnimator backgroundAlpha =
+                CompositorAnimator.ofFloat(handler, 1f, 0f, BACKGROUND_FADING_DURATION_MS,
+                        animator -> mBackgroundAlpha = animator.getAnimatedValue());
+        backgroundAlpha.setInterpolator(CompositorAnimator.FAST_OUT_LINEAR_IN_INTERPOLATOR);
+        animationList.add(backgroundAlpha);
 
         mTabToSwitcherAnimation = new AnimatorSet();
         mTabToSwitcherAnimation.playTogether(animationList);
@@ -355,7 +374,8 @@ public class GridTabSwitcherLayout
                 layerTitleCache, tabContentManager, resourceManager, fullscreenManager,
                 ChromeFeatureList.isEnabled(ChromeFeatureList.TAB_TO_GTS_ANIMATION)
                         ? mGridTabSwitcher.getResourceId()
-                        : 0);
+                        : 0,
+                mBackgroundAlpha);
         mFrameCount++;
         if (mLastFrameTime != 0) {
             long elapsed = SystemClock.elapsedRealtime() - mLastFrameTime;

chrome/browser/android/compositor/scene_layer/tab_list_scene_layer.cc

@@ -203,7 +203,8 @@ void TabListSceneLayer::PutTabLayer(
 void TabListSceneLayer::PutBackgroundLayer(
     JNIEnv* env,
     const base::android::JavaParamRef<jobject>& jobj,
-    jint resource_id) {
+    jint resource_id,
+    jfloat alpha) {
   int ui_resource_id = resource_manager_->GetUIResourceId(
       ui::ANDROID_RESOURCE_TYPE_DYNAMIC, resource_id);
   if (ui_resource_id == 0)
@@ -221,6 +222,7 @@ void TabListSceneLayer::PutBackgroundLayer(
           ->GetResource(ui::ANDROID_RESOURCE_TYPE_DYNAMIC, resource_id)
           ->size();
   background_layer_->SetBounds(size);
+  background_layer_->SetOpacity(alpha);
 }
 
 void TabListSceneLayer::OnDetach() {

chrome/browser/android/compositor/scene_layer/tab_list_scene_layer.h

@@ -110,7 +110,8 @@ class TabListSceneLayer : public SceneLayer {
 
   void PutBackgroundLayer(JNIEnv* env,
                           const base::android::JavaParamRef<jobject>& jobj,
-                          jint resource_id);
+                          jint resource_id,
+                          jfloat alpha);
 
   void OnDetach() override;
   bool ShouldShowBackground() override;