Add support for converting cc::Region to and from protobuf.

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 20 matching lines @@
     # to include protos from other directories/targets (crbug.com/542423).
     "compositor_message.proto",
     "display_item.proto",
     "layer.proto",
     "layer_position_constraint.proto",
     "point.proto",
     "point3f.proto",
     "pointf.proto",
     "rect.proto",
     "rectf.proto",
+    "region.proto",
     "scroll_offset.proto",
     "size.proto",
     "sizef.proto",
     "skregion.proto",
     "skrrect.proto",
     "skxfermode.proto",
     "transform.proto",
     "vector2df.proto",
   ]
 
   deps = [
     "//third_party/protobuf:protobuf_lite",
   ]
 
   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" ]
 }