Add extension permissions for Media Gallery API.

chrome/renderer/resources/extensions/experimental.media_galleries_custom_bindings.js

 // 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.
 
 // Custom bindings for the Media Gallery API.
 
 var mediaGalleriesNatives = requireNative('experimental_mediaGalleries');
 
 var chromeHidden = requireNative('chrome_hidden').GetChromeHidden();
 
 chromeHidden.registerCustomHook('experimental.mediaGalleries',
                                 function(bindingsAPI, extensionId) {
   var apiFunctions = bindingsAPI.apiFunctions;
 
   // getMediaFileSystems uses a custom callback so that it can instantiate and
   // return an array of file system objects.
   apiFunctions.setCustomCallback('getMediaFileSystems',
                                  function(name, request, response) {
-    var result = [];
-    for (var i = 0; i < response.length; i++) {
-      result.push(
-          mediaGalleriesNatives.GetMediaFileSystemObject(response[i].fsid,
-                                                         response[i].dirname));
+    var result = null;
+    if (response) {
+      result = [];
+      for (var i = 0; i < response.length; i++) {
+        result.push(mediaGalleriesNatives.GetMediaFileSystemObject(
+            response[i].fsid, response[i].dirname));
+      }
     }
     if (request.callback)
       request.callback(result);
     request.callback = null;
   });
 
   // extractEmbeddedThumbnails uses a renderer side handler so that it can
   // synchronously return a result.  The result object's state is computable
   // from the function's input.
   apiFunctions.setHandleRequest('extractEmbeddedThumbnails',
                                  function(fileEntry) {
     return mediaGalleriesNatives.ExtractEmbeddedThumbnails(fileEntry);
   });
 });