[Sync] Make ModelSafeWorker a true interface

chrome/browser/sync/engine/model_safe_worker.cc

 // Copyright (c) 2011 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 "chrome/browser/sync/engine/model_safe_worker.h"
 #include "chrome/browser/sync/util/unrecoverable_error_info.h"
 
 #include "base/json/json_writer.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/values.h"
@@ skipping 53 matching lines @@
     case GROUP_PASSIVE:
       return "GROUP_PASSIVE";
     case GROUP_PASSWORD:
       return "GROUP_PASSWORD";
     default:
       NOTREACHED();
       return "INVALID";
   }
 }
 
-ModelSafeWorker::ModelSafeWorker() {}
-
 ModelSafeWorker::~ModelSafeWorker() {}
 
-UnrecoverableErrorInfo ModelSafeWorker::DoWorkAndWaitUntilDone(
-  const WorkCallback& work) {
-  // For GROUP_PASSIVE, we do the work on the current thread.
-  return work.Run();
-}
-
-ModelSafeGroup ModelSafeWorker::GetModelSafeGroup() {
-  return GROUP_PASSIVE;
-}
-
 }  // namespace browser_sync