Add type annotations to metadata_dispatcher.js.

ui/file_manager/externs/platform_worker.js

Index: ui/file_manager/externs/platform_worker.js
diff --git a/ui/file_manager/externs/platform.js b/ui/file_manager/externs/platform_worker.js
similarity index 63%
copy from ui/file_manager/externs/platform.js
copy to ui/file_manager/externs/platform_worker.js
index 476e3d17eb0538674d7a18ffc7cb0cf86de02659..54ed8fc2c74d9260ca32f150a917dc85c805de78 100644
--- a/ui/file_manager/externs/platform.js
+++ b/ui/file_manager/externs/platform_worker.js
@@ -2,12 +2,12 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Externs which are common for all chrome packaged apps.
+// Externs which are common for all worker of chrome packaged apps.
 
 /**
  * @param {string} url
  * @param {function(!Entry)} successCallback
  * @param {function(!FileError)=} opt_errorCallback
  */
-Window.prototype.webkitResolveLocalFileSystemURL =
-    function(url, successCallback, opt_errorCallback) {};
+function webkitResolveLocalFileSystemURL(
+    url, successCallback, opt_errorCallback) {}