Add support for (de)serializing cc::Layer hierarchy.

cc/layers/layer_serializer.cc

+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "cc/layers/layer_serializer.h"
+
+#include "cc/layers/layer.h"
+#include "cc/proto/layer.pb.h"
+
+namespace cc {
+
+// static
+void LayerSerializer::SerializeLayerHierarchy(
+    const scoped_refptr<Layer> root_layer,
+    proto::LayerNode* root_node) {
+  root_layer->ToLayerNodeProto(root_node);
+}
+
+}  // namespace cc