Add SurfaceReference class.

cc/ipc/surface_id_struct_traits.h

 // Copyright 2016 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_IPC_SURFACE_ID_STRUCT_TRAITS_H_
 #define CC_IPC_SURFACE_ID_STRUCT_TRAITS_H_
 
 #include "cc/ipc/frame_sink_id_struct_traits.h"
 #include "cc/ipc/local_frame_id_struct_traits.h"
 #include "cc/ipc/surface_id.mojom-shared.h"
 #include "cc/surfaces/frame_sink_id.h"
+#include "cc/surfaces/local_frame_id.h"
 #include "cc/surfaces/surface_id.h"
 
 namespace mojo {
 
 template <>
 struct StructTraits<cc::mojom::SurfaceIdDataView, cc::SurfaceId> {
   static const cc::FrameSinkId& frame_sink_id(const cc::SurfaceId& id) {
     return id.frame_sink_id();
   }
 
   static const cc::LocalFrameId& local_frame_id(const cc::SurfaceId& id) {
     return id.local_frame_id();
   }
 
   static bool Read(cc::mojom::SurfaceIdDataView data, cc::SurfaceId* out) {
-    cc::FrameSinkId frame_sink_id;
-    if (!data.ReadFrameSinkId(&frame_sink_id))
-      return false;
-
-    cc::LocalFrameId local_frame_id;
-    if (!data.ReadLocalFrameId(&local_frame_id))
-      return false;
-
-    *out = cc::SurfaceId(frame_sink_id, local_frame_id);
-    return true;
+    return data.ReadFrameSinkId(&out->frame_sink_id_) &&
+           data.ReadLocalFrameId(&out->local_frame_id_);
   }
 };
 
 }  // namespace mojo
 
 #endif  // CC_IPC_SURFACE_ID_STRUCT_TRAITS_H_