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

cc/layers/layer_deserializer.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_deserializer.h"
+
+#include "base/stl_util.h"
+#include "cc/layers/layer.h"
+#include "cc/layers/layer_proto_factory.h"
+#include "cc/proto/layer.pb.h"
+
+namespace cc {
+
+LayerDeserializer::LayerDeserializer() {}
+
+LayerDeserializer::~LayerDeserializer() {}
+
+// static
+scoped_refptr<Layer> LayerDeserializer::DeserializeLayerHierarchy(
+    scoped_refptr<Layer> existing_root,
+    const proto::LayerNode& root_node) {
+  LayerIdMap layer_id_map;
+  RecursivelyFindAllLayers(existing_root, &layer_id_map);
+
+  scoped_refptr<Layer> new_root = existing_root;
+  if (!existing_root ||
+      (root_node.has_id() && root_node.id() != (uint32)existing_root->id())) {

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

no c-style casts, is the type of the id in the proto different from the type in
the class? Why is it different?

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

My bad. Fixed proto.

+    // The root node has changed or there was no root node,
+    // so find or create the new root.
+    new_root =
+        LayerProtoFactory::FindOrAllocateAndConstruct(root_node, layer_id_map);
+  }
+  new_root->FromLayerNodeProto(root_node, layer_id_map);
+  return new_root;
+}
+
+// static
+void LayerDeserializer::RecursivelyFindAllLayers(scoped_refptr<Layer> layer,

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

Can you use LayerTreeHostComon::CallFunctionForSubtree instead?

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

Awesome! Thanks!

+                                                 LayerIdMap* layer_id_map) {
+  (*layer_id_map)[layer->id()] = layer;
+  for (auto child : layer->children()) {
+    RecursivelyFindAllLayers(child, layer_id_map);
+  }
+
+  if (layer->mask_layer())
+    RecursivelyFindAllLayers(layer->mask_layer(), layer_id_map);
+  if (layer->replica_layer())
+    RecursivelyFindAllLayers(layer->replica_layer(), layer_id_map);
+}
+
+}  // namespace cc