sync: Use a single transaction in ProcessUpdates rather than one per entry.

chrome/browser/sync/engine/process_updates_command.h

 // Copyright (c) 2006-2009 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 CHROME_BROWSER_SYNC_ENGINE_PROCESS_UPDATES_COMMAND_H_
 #define CHROME_BROWSER_SYNC_ENGINE_PROCESS_UPDATES_COMMAND_H_
 #pragma once
 
 #include "chrome/browser/sync/engine/model_changing_syncer_command.h"
 #include "chrome/browser/sync/engine/syncer_types.h"
 
 namespace syncable {
 class ScopedDirLookup;
+class WriteTransaction;
 }
 
 namespace sync_pb {
 class SyncEntity;
 }
 
 namespace browser_sync {
 
 // A syncer command for processing updates.
 //
 // Preconditions - updates in the SyncerSesssion have been downloaded
 //                 and verified.
 //
 // Postconditions - All of the verified SyncEntity data will be copied to
 //                  the server fields of the corresponding syncable entries.
 // TODO(tim): This should not be ModelChanging (bug 36592).
 class ProcessUpdatesCommand : public ModelChangingSyncerCommand {
  public:
   ProcessUpdatesCommand();
   virtual ~ProcessUpdatesCommand();
 
   // ModelChangingSyncerCommand implementation.
   virtual bool ModelNeutralExecuteImpl(sessions::SyncSession* session);
   virtual void ModelChangingExecuteImpl(sessions::SyncSession* session);
 
  private:
   ServerUpdateProcessingResult ProcessUpdate(
       const syncable::ScopedDirLookup& dir,
-      const sync_pb::SyncEntity& proto_update);
+      const sync_pb::SyncEntity& proto_update,
+      syncable::WriteTransaction* const trans);
   DISALLOW_COPY_AND_ASSIGN(ProcessUpdatesCommand);
 };
 
 }  // namespace browser_sync
 
 #endif  // CHROME_BROWSER_SYNC_ENGINE_PROCESS_UPDATES_COMMAND_H_