Add SurfaceReference class.

cc/ipc/local_frame_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_LOCAL_FRAME_ID_STRUCT_TRAITS_H_
 #define CC_IPC_LOCAL_FRAME_ID_STRUCT_TRAITS_H_
 
 #include "cc/ipc/local_frame_id.mojom-shared.h"
 #include "cc/surfaces/local_frame_id.h"
 #include "mojo/common/common_custom_types_struct_traits.h"
 
 namespace mojo {
 
 template <>
 struct StructTraits<cc::mojom::LocalFrameIdDataView, cc::LocalFrameId> {
   static uint32_t local_id(const cc::LocalFrameId& local_frame_id) {
     return local_frame_id.local_id();
   }
 
   static const base::UnguessableToken& nonce(
       const cc::LocalFrameId& local_frame_id) {
     return local_frame_id.nonce();
   }
 
   static bool Read(cc::mojom::LocalFrameIdDataView data,
                    cc::LocalFrameId* out) {
-    base::UnguessableToken nonce;
-    if (!data.ReadNonce(&nonce))
-      return false;
-
-    *out = cc::LocalFrameId(data.local_id(), nonce);
-    return true;
+    out->local_id_ = data.local_id();
+    return data.ReadNonce(&out->nonce_);
   }
 };
 
 }  // namespace mojo
 
 #endif  // CC_IPC_LOCAL_FRAME_ID_STRUCT_TRAITS_H_