Add GetURLForBrowserTab method to the external file system backend.

chrome/browser/chromeos/file_system_provider/fileapi/backend_delegate.h

 // 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.
 
 #ifndef CHROME_BROWSER_CHROMEOS_FILE_SYSTEM_PROVIDER_FILEAPI_BACKEND_DELEGATE_H_
 #define CHROME_BROWSER_CHROMEOS_FILE_SYSTEM_PROVIDER_FILEAPI_BACKEND_DELEGATE_H_
 
 #include "base/basictypes.h"
 #include "base/file_util.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 25 matching lines @@
       const storage::FileSystemURL& url,
       int64 offset,
       const base::Time& expected_modification_time,
       storage::FileSystemContext* context) OVERRIDE;
   virtual scoped_ptr<storage::FileStreamWriter> CreateFileStreamWriter(
       const storage::FileSystemURL& url,
       int64 offset,
       storage::FileSystemContext* context) OVERRIDE;
   virtual storage::WatcherManager* GetWatcherManager(
       const storage::FileSystemURL& url) OVERRIDE;
+  virtual void GetAlternativeURL(
+      const storage::FileSystemURL& url,
+      base::Callback<void(const GURL& url)> callback) OVERRIDE;
 
  private:
   scoped_ptr<storage::AsyncFileUtil> async_file_util_;
 
   DISALLOW_COPY_AND_ASSIGN(BackendDelegate);
 };
 
 }  // namespace file_system_provider
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_FILE_SYSTEM_PROVIDER_FILEAPI_BACKEND_DELEGATE_H_