CC Animation: Use ElementId to attach CC animation players.

cc/test/layer_test_common.cc

Index: cc/test/layer_test_common.cc
diff --git a/cc/test/layer_test_common.cc b/cc/test/layer_test_common.cc
index 4ba0927d230b2e1fc013c756d83fbee2c3d756b4..2998dae4fc526322d370852bca01d2763df7afed 100644
--- a/cc/test/layer_test_common.cc
+++ b/cc/test/layer_test_common.cc
@@ -127,6 +127,7 @@ LayerTestCommon::LayerImplTest::LayerImplTest(const LayerTreeSettings& settings)
       layer_impl_id_(2) {
   std::unique_ptr<LayerImpl> root =
       LayerImpl::Create(host_->host_impl()->active_tree(), 1);
+  root->SetElementId(NextElementId());
   host_->host_impl()->active_tree()->SetRootLayer(std::move(root));
   root_layer()->SetHasRenderSurface(true);
   host_->host_impl()->SetVisible(true);