Just update the content if frame animation is already running.

This is a workaround for crbug.com/1134279, but probably better way to
handle this particular situation because the animation layer will fade out w/o
interruption and a user will see the final state.

DefaultFrameHeader.AnimateDuringAnimation

Bug: 1132276, 1126857, 1134279
Test: manual (see bug for reprostep),
Change-Id: I31c0281983f52a4d181addf8c522e1efa5eeddcf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2442378Reviewed-by: Malay Keshav <malaykeshav@chromium.org>
Reviewed-by: Alexander Alekseev <alemate@chromium.org>
Commit-Queue: Mitsuru Oshima <oshima@chromium.org>
Cr-Commit-Position: refs/heads/master@{#812979}

ash/frame/default_frame_header_unittest.cc

@@ -279,4 +279,31 @@ TEST_F(DefaultFrameHeaderTest, ResizeAndReorderDuringAnimation) {
   }
 }
 
+// Make sure that the animation request while animating will not
+// create another animation.
+TEST_F(DefaultFrameHeaderTest, AnimateDuringAnimation) {
+  const auto bounds = gfx::Rect(100, 100);
+  auto win_0 = CreateAppWindow(bounds, AppType::BROWSER);
+  // A frame will not animate until it is painted first.
+  FramePaintWaiter(win_0.get()).Wait();
+
+  auto* widget = Widget::GetWidgetForNativeWindow(win_0.get());
+
+  auto lock = widget->LockPaintAsActive();
+  auto win_1 = CreateAppWindow(bounds, AppType::BROWSER);
+  FramePaintWaiter(win_1.get()).Wait();
+
+  EXPECT_TRUE(wm::IsActiveWindow(win_1.get()));
+
+  ui::ScopedAnimationDurationScaleMode non_zero_duration_mode(
+      ui::ScopedAnimationDurationScaleMode::NON_ZERO_DURATION);
+
+  auto layer_bounds = win_0->layer()->bounds();
+  lock.reset();
+  win_1.reset();
+  EXPECT_TRUE(wm::IsActiveWindow(win_0.get()));
+  // Makes sure that the layer has full damaged bounds.
+  EXPECT_TRUE(win_0->layer()->damaged_region().Contains(layer_bounds));
+}
+
 }  // namespace ash

ash/public/cpp/frame_header.cc

@@ -112,7 +112,12 @@ class FrameHeader::FrameAnimatorView : public views::View,
   }
 
   void StartAnimation(base::TimeDelta duration) {
-    StopAnimation();
+    if (layer_owner_) {
+      // If animation is already running, just update the content of the new
+      // layer.
+      parent_->SchedulePaint();
+      return;
+    }
     aura::Window* window = frame_header_->target_widget()->GetNativeWindow();
 
     // Make sure the this view is at the bottom of root view's children.