Add the "virtual" keyword on method overrides that are missing it.

chrome/browser/sync/glue/history_model_worker.h

 // Copyright (c) 2010 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_GLUE_HISTORY_MODEL_WORKER_H_
 #define CHROME_BROWSER_SYNC_GLUE_HISTORY_MODEL_WORKER_H_
 #pragma once
 
 #include "chrome/browser/sync/engine/model_safe_worker.h"
 
@@ skipping 12 matching lines @@
 
 // A ModelSafeWorker for history models that accepts requests
 // from the syncapi that need to be fulfilled on the history thread.
 class HistoryModelWorker : public browser_sync::ModelSafeWorker,
                            public CancelableRequestConsumerBase {
  public:
   explicit HistoryModelWorker(HistoryService* history_service);
   virtual ~HistoryModelWorker();
 
   // ModelSafeWorker implementation. Called on syncapi SyncerThread.
-  void DoWorkAndWaitUntilDone(Callback0::Type* work);
+  virtual void DoWorkAndWaitUntilDone(Callback0::Type* work);
   virtual ModelSafeGroup GetModelSafeGroup() { return GROUP_HISTORY; }
   virtual bool CurrentThreadIsWorkThread();
 
   // CancelableRequestConsumerBase implementation.
   virtual void OnRequestAdded(CancelableRequestProvider* provider,
                               CancelableRequestProvider::Handle handle) {}
 
   virtual void OnRequestRemoved(CancelableRequestProvider* provider,
                                 CancelableRequestProvider::Handle handle) {}
 
   virtual void WillExecute(CancelableRequestProvider* provider,
                            CancelableRequestProvider::Handle handle) {}
 
   virtual void DidExecute(CancelableRequestProvider* provider,
                           CancelableRequestProvider::Handle handle) {}
 
  private:
   scoped_refptr<HistoryService> history_service_;
   DISALLOW_COPY_AND_ASSIGN(HistoryModelWorker);
 };
 
 }  // namespace browser_sync
 
 #endif  // CHROME_BROWSER_SYNC_GLUE_HISTORY_MODEL_WORKER_H_