Fix ExtensionServiceTest.ClearExtensionData flakiness

chrome/browser/extensions/data_deleter.h

 // 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.
 
 #ifndef CHROME_BROWSER_EXTENSIONS_DATA_DELETER_H_
 #define CHROME_BROWSER_EXTENSIONS_DATA_DELETER_H_
 
 #include <string>
 #include "base/basictypes.h"
+#include "base/callback_forward.h"
 
 class Profile;
 
 namespace extensions {
 
 class Extension;
 
 class DataDeleter {
  public:
   // Starts removing data. The extension should not be running when this is
   // called. Cookies are deleted on the current thread, local storage and
   // databases/settings are deleted asynchronously on the webkit and file
   // threads, respectively. This function must be called from the UI thread.
-  static void StartDeleting(Profile* profile, const Extension* extenion);
+  //
+  // |callback| is called when data deletion is done or at least the deletion
+  // is scheduled.
+  static void StartDeleting(Profile* profile,
+                            const Extension* extenion,
+                            const base::Closure& callback);
 
   DISALLOW_COPY_AND_ASSIGN(DataDeleter);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_DATA_DELETER_H_