[Sync] Initial USS service implementation for DeviceInfo.

components/sync_driver/device_info_sync_service.cc

 // Copyright 2014 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.
 
 #include "components/sync_driver/device_info_sync_service.h"
 
 #include "base/metrics/histogram_macros.h"
 #include "base/strings/stringprintf.h"
 #include "components/sync_driver/local_device_info_provider.h"
 #include "sync/api/sync_change.h"
@@ skipping 343 matching lines @@
   const sync_pb::DeviceInfoSpecifics& specifics = entity.device_info();
 
   std::string local_device_tag =
       base::StringPrintf("DeviceInfo_%s", specifics.cache_guid().c_str());
 
   return SyncData::CreateLocalData(
       local_device_tag, specifics.client_name(), entity);
 }
 
 DeviceInfo* DeviceInfoSyncService::CreateDeviceInfo(
-    const syncer::SyncData sync_data) {
+    const syncer::SyncData& sync_data) {
   const sync_pb::DeviceInfoSpecifics& specifics =
       sync_data.GetSpecifics().device_info();
 
   return new DeviceInfo(specifics.cache_guid(),
                         specifics.client_name(),
                         specifics.chrome_version(),
                         specifics.sync_user_agent(),
                         specifics.device_type(),
                         specifics.signin_scoped_device_id());
 }
@@ skipping 10 matching lines @@
   SyncDataMap::iterator iter = all_data_.find(client_id);
   if (iter != all_data_.end()) {
     DVLOG(1) << "Deleting DEVICE_INFO for "
              << iter->second.GetSpecifics().device_info().client_name()
              << " with ID " << client_id;
     all_data_.erase(iter);
   }
 }
 
 }  // namespace sync_driver