Change platform app api getDisplayPath to take FileEntry.

chrome/common/extensions/api/file_system.idl

 // Copyright (c) 2012 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.
 
 // File-level comment to appease parser. Eventually this will not be necessary.
 
 [nodoc] namespace fileSystem {
   callback GetDisplayPathCallback = void (DOMString displayPath);
 
   interface Functions {
-    static void getDisplayPath(DOMString fsname, DOMString fspath,
+    static void getDisplayPath([instanceOf=FileEntry] object fileEntry,
                                GetDisplayPathCallback onSuccess);
   };
 };