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

cc/layers/layer_proto_converter.cc

Index: cc/layers/layer_proto_converter.cc
diff --git a/cc/layers/layer_proto_converter.cc b/cc/layers/layer_proto_converter.cc
new file mode 100644
index 0000000000000000000000000000000000000000..2dcc3d90a441209006cffd8f9fc55a3fc6bd4610
--- /dev/null
+++ b/cc/layers/layer_proto_converter.cc
@@ -0,0 +1,72 @@
+// 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_proto_converter.h"
+
+#include "base/stl_util.h"
+#include "cc/layers/layer.h"
+#include "cc/proto/layer.pb.h"
+#include "cc/trees/layer_tree_host_common.h"
+#include "cc/trees/layer_tree_settings.h"
+
+namespace cc {
+
+LayerProtoConverter::LayerProtoConverter() {}
+
+LayerProtoConverter::~LayerProtoConverter() {}
+
+// static
+void LayerProtoConverter::SerializeLayerHierarchy(
+    const scoped_refptr<Layer> root_layer,
+    proto::LayerNode* root_node) {
+  root_layer->ToLayerNodeProto(root_node);
+}
+
+// static
+scoped_refptr<Layer> LayerProtoConverter::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() != existing_root->id())) {
+    // The root node has changed or there was no root node,
+    // so find or create the new root.
+    new_root = FindOrAllocateAndConstruct(root_node, layer_id_map);
+  }
+  new_root->FromLayerNodeProto(root_node, layer_id_map);
+  return new_root;
+}
+
+// static
+void LayerProtoConverter::RecursivelyFindAllLayers(
+    const scoped_refptr<Layer>& layer,
+    LayerIdMap* layer_id_map) {
+  LayerTreeHostCommon::CallFunctionForSubtree(
+      layer.get(),
+      [layer_id_map](Layer* layer) { (*layer_id_map)[layer->id()] = layer; });
+}
+
+// static
+scoped_refptr<Layer> LayerProtoConverter::FindOrAllocateAndConstruct(
+    const proto::LayerNode& proto,
+    const Layer::LayerIdMap& layer_id_map) {
+  DCHECK(proto.has_id());
+  Layer::LayerIdMap::const_iterator iter = layer_id_map.find(proto.id());
+  if (iter != layer_id_map.end())
+    return iter->second;
+  DCHECK(proto.has_type());
+  switch (proto.type()) {
+    case proto::Base:
+      return Layer::Create(LayerSettings()).get();
+  }
+  // TODO(nyquist): Add the rest of the necessary LayerTypes. This function
+  // should not return null.
+  NOTREACHED();
+  return nullptr;
+}
+
+}  // namespace cc