CC Animation: Use ElementId to attach CC animation players.

cc/test/layer_tree_test.cc

Index: cc/test/layer_tree_test.cc
diff --git a/cc/test/layer_tree_test.cc b/cc/test/layer_tree_test.cc
index 7275ec3a70a98de49c452c8023199dcc16b45047..9ff4005d2b1c1496e227b649ccde923ae5a87185 100644
--- a/cc/test/layer_tree_test.cc
+++ b/cc/test/layer_tree_test.cc
@@ -736,6 +736,7 @@ void LayerTreeTest::DoBeginTest() {
 void LayerTreeTest::SetupTree() {
   if (!layer_tree_host_->root_layer()) {
     scoped_refptr<Layer> root_layer = Layer::Create();
+    root_layer->SetElementId(NextElementId());
     root_layer->SetBounds(gfx::Size(1, 1));
     layer_tree_host_->SetRootLayer(root_layer);
   }
@@ -752,6 +753,12 @@ void LayerTreeTest::Timeout() {
   EndTest();
 }
 
+scoped_refptr<Layer> LayerTreeTest::CreateTestLayer() {
+  auto layer = Layer::Create();
+  layer->SetElementId(NextElementId());
+  return layer;
+}
+
 void LayerTreeTest::RealEndTest() {
   // TODO(mithro): Make this method only end when not inside an impl frame.
   bool main_frame_will_happen;