Add support for (de)serializing LayerTreeHost.

cc/proto/BUILD.gn

 # 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.
 
 import("//third_party/protobuf/proto_library.gni")
 
 # Use a group here to allow external targets to depend on "cc/proto" instead of
 # cc/proto:cc_proto.  We need a group because other component targets are named
 # "proto" which breaks component builds.  A group doesn't have the same issue.
 group("proto") {
@@ skipping 18 matching lines @@
   sources = [
     # TODO(dtrainor): Move protos to their correct packages once it's possible
     # to include protos from other directories/targets (crbug.com/542423).
     "compositor_message.proto",
     "display_item.proto",
     "display_list_recording_source.proto",
     "layer.proto",
     "layer_position_constraint.proto",
     "layer_selection_bound.proto",
     "layer_tree_debug_state.proto",
+    "layer_tree_host.proto",
     "layer_tree_settings.proto",
     "managed_memory_policy.proto",
     "memory_allocation.proto",
     "point.proto",
     "point3f.proto",
     "pointf.proto",
     "property_tree.proto",
     "rect.proto",
     "rectf.proto",
     "region.proto",
@@ skipping 13 matching lines @@
   ]
 
   cc_generator_options = "dllexport_decl=CC_PROTO_EXPORT:"
   cc_include = "cc/proto/cc_proto_export.h"
 
   defines = [ "CC_PROTO_IMPLEMENTATION" ]
 
   # Warn if clang creates exit destructors.
   extra_configs = [ "//build/config/compiler:wexit_time_destructors" ]
 }