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

cc/layers/layer_deserializer.h

+// 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.
+
+#ifndef CC_LAYERS_LAYER_DESERIALIZER_H_
+#define CC_LAYERS_LAYER_DESERIALIZER_H_
+
+#include "base/macros.h"
+#include "cc/base/cc_export.h"
+#include "cc/layers/layer.h"
+
+namespace cc {
+
+namespace proto {
+class LayerNode;
+class LayerUpdate;
+}
+
+// A class to faciliate deserialization of a Layer tree.
+class CC_EXPORT LayerDeserializer {
+ public:
+  // Recursively iterate over the given LayerNode proto and read the structure
+  // into a local Layer structure, re-using existing Layers. returns the new
+  // root Layer after updating the hierarchy (may be the same as
+  // |existing_root|).
+  static scoped_refptr<Layer> DeserializeLayerHierarchy(
+      scoped_refptr<Layer> existing_root,
+      const proto::LayerNode& root_node);
+
+ private:
+  LayerDeserializer();
+  virtual ~LayerDeserializer();
+
+  typedef base::hash_map<int, scoped_refptr<Layer>> LayerIdMap;
+  // Start at |layer| and recursively add |layer| and all its children and
+  // special layers to |layer_id_map|.
+  static void RecursivelyFindAllLayers(const scoped_refptr<Layer> layer,

[vmpstr, 2015/10/21 22:34:14]

const scoped_refptr<Layer>& layer?

[nyquist, 2015/10/23 00:12:30]

Done.

+                                       LayerIdMap* layer_id_map);
+
+  DISALLOW_COPY_AND_ASSIGN(LayerDeserializer);
+};
+
+}  // namespace cc
+
+#endif  // CC_LAYERS_LAYER_DESERIALIZER_H_