Add GetURLForBrowserTab method to the external file system backend.

chrome/browser/chromeos/fileapi/file_system_backend_delegate.h

 // Copyright 2013 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_FILEAPI_FILE_SYSTEM_BACKEND_DELEGATE_H_
 #define CHROME_BROWSER_CHROMEOS_FILEAPI_FILE_SYSTEM_BACKEND_DELEGATE_H_
 
 #include "base/basictypes.h"
+#include "base/callback.h"
 #include "base/memory/scoped_ptr.h"
 #include "webkit/common/fileapi/file_system_types.h"
 
+class GURL;
+
 namespace base {
 class Time;
 }  // namespace base
 
 namespace storage {
 class AsyncFileUtil;
 class FileSystemContext;
 class FileStreamReader;
 class FileSystemURL;
 class FileStreamWriter;
@@ skipping 26 matching lines @@
   // Called from FileSystemBackend::CreateFileStreamWriter().
   virtual scoped_ptr<storage::FileStreamWriter> CreateFileStreamWriter(
       const storage::FileSystemURL& url,
       int64 offset,
       storage::FileSystemContext* context) = 0;
 
   // Called from the FileSystemWatcherService class. The returned pointer must
   // stay valid until shutdown.
   virtual storage::WatcherManager* GetWatcherManager(
       const storage::FileSystemURL& url) = 0;
+
+  // Called from FileSystemBackend::GetAlternativeURL.
+  virtual void GetAlternativeURL(
+      const storage::FileSystemURL& url,
+      base::Callback<void(const GURL& url)> callback) = 0;
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_FILEAPI_FILE_SYSTEM_BACKEND_DELEGATE_H_