Revert of Use element id's for animations

cc/test/animation_timelines_test_common.h

Index: cc/test/animation_timelines_test_common.h
diff --git a/cc/test/animation_timelines_test_common.h b/cc/test/animation_timelines_test_common.h
index d020257b2eadbd8a339c2d110852e1ef21b63ab2..914385d248cb2e1c083e1d9eaf3f8c7494797ae1 100644
--- a/cc/test/animation_timelines_test_common.h
+++ b/cc/test/animation_timelines_test_common.h
@@ -192,10 +192,10 @@
  private:
   std::unique_ptr<AnimationHost> host_;
 
-  using ElementIdToTestLayer =
-      std::unordered_map<ElementId, std::unique_ptr<TestLayer>, ElementIdHash>;
-  ElementIdToTestLayer layers_in_active_tree_;
-  ElementIdToTestLayer layers_in_pending_tree_;
+  using LayerIdToTestLayer =
+      std::unordered_map<int, std::unique_ptr<TestLayer>>;
+  LayerIdToTestLayer layers_in_active_tree_;
+  LayerIdToTestLayer layers_in_pending_tree_;
 
   gfx::ScrollOffset scroll_offset_;
   bool mutators_need_commit_;
@@ -264,7 +264,7 @@
   void AnimateLayersTransferEvents(base::TimeTicks time,
                                    unsigned expect_events);
 
-  AnimationPlayer* GetPlayerForElementId(ElementId element_id);
+  AnimationPlayer* GetPlayerForLayerId(ElementId element_id);
   AnimationPlayer* GetImplPlayerForLayerId(ElementId element_id);
 
   int NextTestLayerId();
@@ -277,7 +277,7 @@
 
   const int timeline_id_;
   const int player_id_;
-  ElementId element_id_;
+  int element_id_;
 
   int next_test_layer_id_;