Add GetURLForBrowserTab method to the external file system backend.

chrome/browser/chromeos/fileapi/file_system_backend.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_H_
 #define CHROME_BROWSER_CHROMEOS_FILEAPI_FILE_SYSTEM_BACKEND_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 113 matching lines @@
   virtual std::vector<base::FilePath> GetRootDirectories() const OVERRIDE;
   virtual void GrantFullAccessToExtension(
       const std::string& extension_id) OVERRIDE;
   virtual void GrantFileAccessToExtension(
       const std::string& extension_id,
       const base::FilePath& virtual_path) OVERRIDE;
   virtual void RevokeAccessForExtension(
       const std::string& extension_id) OVERRIDE;
   virtual bool GetVirtualPath(const base::FilePath& filesystem_path,
                               base::FilePath* virtual_path) OVERRIDE;
+  virtual void GetAlternativeURL(
+      const storage::FileSystemURL& url,
+      base::Callback<void(const GURL& url)>) OVERRIDE;
 
  private:
   scoped_refptr<storage::SpecialStoragePolicy> special_storage_policy_;
   scoped_ptr<FileAccessPermissions> file_access_permissions_;
   scoped_ptr<storage::AsyncFileUtil> local_file_util_;
 
   // The delegate instance for the drive file system related operations.
   scoped_ptr<FileSystemBackendDelegate> drive_delegate_;
 
   // The delegate instance for the provided file system related operations.
@@ skipping 18 matching lines @@
   // Globally visible mount points. System MountPonts instance should outlive
   // all FileSystemBackend instances, so raw pointer is safe.
   storage::ExternalMountPoints* system_mount_points_;
 
   DISALLOW_COPY_AND_ASSIGN(FileSystemBackend);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_FILEAPI_FILE_SYSTEM_BACKEND_H_