Add GetURLForBrowserTab method to the external file system backend.

chrome/browser/chromeos/drive/fileapi/file_system_backend_delegate.h

Index: chrome/browser/chromeos/drive/fileapi/file_system_backend_delegate.h
diff --git a/chrome/browser/chromeos/drive/fileapi/file_system_backend_delegate.h b/chrome/browser/chromeos/drive/fileapi/file_system_backend_delegate.h
index ea701cb3e00dd267a27e00191afe0c6a0ba17dc4..ef88438f855eca070c148a02e9ef4c334f90836c 100644
--- a/chrome/browser/chromeos/drive/fileapi/file_system_backend_delegate.h
+++ b/chrome/browser/chromeos/drive/fileapi/file_system_backend_delegate.h
@@ -41,6 +41,9 @@ class FileSystemBackendDelegate : public chromeos::FileSystemBackendDelegate {
       storage::FileSystemContext* context) OVERRIDE;
   virtual storage::WatcherManager* GetWatcherManager(
       const storage::FileSystemURL& url) OVERRIDE;
+  virtual void GetURLForBrowserTab(
+      const storage::FileSystemURL& url,
+      const base::Callback<void(const GURL& url)>& callback) OVERRIDE;
 
  private:
   scoped_ptr<storage::AsyncFileUtil> async_file_util_;