StructTraits optimizations

cc/ipc/returned_resource_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_RETURNED_RESOURCE_STRUCT_TRAITS_H_
 #define CC_IPC_RETURNED_RESOURCE_STRUCT_TRAITS_H_
 
 #include "cc/ipc/returned_resource.mojom.h"
 #include "cc/resources/returned_resource.h"
 
 namespace mojo {
 
 template <>
 struct StructTraits<cc::mojom::ReturnedResource, cc::ReturnedResource> {
   static uint32_t id(const cc::ReturnedResource& resource) {
     return resource.id;
   }
 
-  static gpu::SyncToken sync_token(const cc::ReturnedResource& resource) {
+  static const gpu::SyncToken& sync_token(
+      const cc::ReturnedResource& resource) {
     return resource.sync_token;
   }
 
   static int32_t count(const cc::ReturnedResource& resource) {
     return resource.count;
   }
 
   static bool lost(const cc::ReturnedResource& resource) {
     return resource.lost;
   }
 
   static bool Read(cc::mojom::ReturnedResourceDataView data,
                    cc::ReturnedResource* out) {
     if (!data.ReadSyncToken(&out->sync_token))
       return false;
     out->id = data.id();
     out->count = data.count();
     out->lost = data.lost();
     return true;
   }
 };
 
 }  // namespace mojo
 
 #endif  // CC_IPC_RETURNED_RESOURCE_STRUCT_TRAITS_H_