CC Animation: Use ElementId to attach CC animation players.

cc/test/fake_picture_layer.h

Index: cc/test/fake_picture_layer.h
diff --git a/cc/test/fake_picture_layer.h b/cc/test/fake_picture_layer.h
index 038e97543d9ad206f0750f812363b93bf481d5f8..75089eaf5eb4cc6d4a67a18c050e93626938b635 100644
--- a/cc/test/fake_picture_layer.h
+++ b/cc/test/fake_picture_layer.h
@@ -12,18 +12,24 @@
 #include "base/memory/ref_counted.h"
 #include "cc/layers/picture_layer.h"
 #include "cc/playback/recording_source.h"
+#include "cc/test/test_element_id.h"
 
 namespace cc {
 class FakePictureLayer : public PictureLayer {
  public:
   static scoped_refptr<FakePictureLayer> Create(ContentLayerClient* client) {
-    return make_scoped_refptr(new FakePictureLayer(client));
+    auto layer = make_scoped_refptr(new FakePictureLayer(client));
+    layer->SetElementId(NextTestElementId());
+    return layer;
   }
 
   static scoped_refptr<FakePictureLayer> CreateWithRecordingSource(
       ContentLayerClient* client,
       std::unique_ptr<RecordingSource> source) {
-    return make_scoped_refptr(new FakePictureLayer(client, std::move(source)));
+    auto layer =
+        make_scoped_refptr(new FakePictureLayer(client, std::move(source)));
+    layer->SetElementId(NextTestElementId());
+    return layer;
   }
 
   std::unique_ptr<LayerImpl> CreateLayerImpl(LayerTreeImpl* tree_impl) override;