CC Animations: Fix the case when main-thread player changes layer_id.

cc/animation/animation_player_unittest.cc

Index: cc/animation/animation_player_unittest.cc
diff --git a/cc/animation/animation_player_unittest.cc b/cc/animation/animation_player_unittest.cc
index 466964f6d7741bf898e8133b07254e6a1373d495..d8030b3ec804a5da9239f5bc2de660ce8c5fcf15 100644
--- a/cc/animation/animation_player_unittest.cc
+++ b/cc/animation/animation_player_unittest.cc
@@ -332,5 +332,39 @@ TEST_F(AnimationPlayerTest, AddRemoveAnimationCausesSetNeedsCommit) {
   client_.set_mutators_need_commit(false);
 }
 
+// If main-thread player switches to another layer within one frame then
+// impl-thread player must be switched as well.
+TEST_F(AnimationPlayerTest, SwitchToLayer) {
+  host_->AddAnimationTimeline(timeline_);
+  timeline_->AttachPlayer(player_);
+  player_->AttachLayer(layer_id_);
+
+  host_->PushPropertiesTo(host_impl_);
+
+  GetImplTimelineAndPlayerByID();
+
+  EXPECT_EQ(player_, GetPlayerForLayerId(layer_id_));
+  EXPECT_TRUE(player_->element_animations());
+  EXPECT_EQ(player_->layer_id(), layer_id_);
+
+  EXPECT_EQ(player_impl_, GetImplPlayerForLayerId(layer_id_));
+  EXPECT_TRUE(player_impl_->element_animations());
+  EXPECT_EQ(player_impl_->layer_id(), layer_id_);
+
+  const int new_layer_id = NextTestLayerId();
+  player_->DetachLayer();
+  player_->AttachLayer(new_layer_id);
+
+  EXPECT_EQ(player_, GetPlayerForLayerId(new_layer_id));
+  EXPECT_TRUE(player_->element_animations());
+  EXPECT_EQ(player_->layer_id(), new_layer_id);
+
+  host_->PushPropertiesTo(host_impl_);
+
+  EXPECT_EQ(player_impl_, GetImplPlayerForLayerId(new_layer_id));
+  EXPECT_TRUE(player_impl_->element_animations());
+  EXPECT_EQ(player_impl_->layer_id(), new_layer_id);
+}
+
 }  // namespace
 }  // namespace cc