Stop unexpected animation during CLEAR_ALL_STACKED

Clear all notification animation consists of two phases:
CLEAR_ALL_STACKED and CLEAR_ALL_VISIBLE.

During CLEAR_ALL_STACKED phase, only the counter at the top should
animate, so each notification should not move even though
GetCurrentValue() might not return 1.0.
See the bug for detail.

TEST=UnifiedMessageListViewTest.ClearAllWithStackingNotifications
BUG=908782

Change-Id: I24f369753cc17ad761d85c654743504a07e9e148
Reviewed-on: https://chromium-review.googlesource.com/c/1352111Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Commit-Queue: Tetsui Ohkubo <tetsui@chromium.org>
Cr-Commit-Position: refs/heads/master@{#611510}

ash/system/message_center/unified_message_list_view.cc

@@ -485,6 +485,11 @@ void UnifiedMessageListView::UpdateClearAllAnimation() {
       DeleteRemovedNotifications();
       UpdateBounds();
       start_height_ = ideal_height_;
+      for (int i = 0; i < child_count(); ++i) {
+        auto* view = GetContainer(i);
+        view->set_start_bounds(view->ideal_bounds());
+      }
+
       PreferredSizeChanged();
 
       state_ = State::CLEAR_ALL_STACKED;

ash/system/message_center/unified_message_list_view_unittest.cc

@@ -443,8 +443,10 @@ TEST_F(UnifiedMessageListViewTest, ClearAllWithStackingNotifications) {
 
   message_list_view()->set_stacked_notification_count(1);
   int previous_height = message_list_view()->GetPreferredSize().height();
+  gfx::Rect previous_bounds = GetMessageViewBounds(1);
   AnimateToMiddle();
   EXPECT_EQ(previous_height, message_list_view()->GetPreferredSize().height());
+  EXPECT_EQ(previous_bounds, GetMessageViewBounds(1));
   AnimateToEnd();
   EXPECT_EQ(1, message_list_view()->child_count());
 
@@ -455,7 +457,7 @@ TEST_F(UnifiedMessageListViewTest, ClearAllWithStackingNotifications) {
   AnimateToEnd();
   EXPECT_EQ(1, message_list_view()->child_count());
 
-  gfx::Rect previous_bounds = GetMessageViewBounds(0);
+  previous_bounds = GetMessageViewBounds(0);
   AnimateToMiddle();
   EXPECT_LT(previous_bounds.x(), GetMessageViewBounds(0).x());
   AnimateToEnd();