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..6b235e77de7d563f4581e017a31bdc3cf156ebbe 100644
--- a/cc/test/fake_picture_layer.h
+++ b/cc/test/fake_picture_layer.h
@@ -17,13 +17,18 @@ 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(NextElementId());
+    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(NextElementId());
+    return layer;
   }
 
   std::unique_ptr<LayerImpl> CreateLayerImpl(LayerTreeImpl* tree_impl) override;