MD Settings: Allow controlled-button to be used with icons.

chrome/browser/resources/settings/downloads_page/downloads_page.js

 // Copyright 2015 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.
 
 /**
  * @fileoverview
  * 'settings-downloads-page' is the settings page containing downloads
  * settings.
  *
  * Example:
@@ skipping 14 matching lines @@
     prefs: {
       type: Object,
       notify: true,
     },
 
     /**
      * Dictionary defining page visibility.
      * @type {!DownloadsPageVisibility}
      */
     pageVisibility: Object,
+
+    /** @private */
+    isControlled_: {
+      type: Boolean,
+      notify: true
+    }
   },
 
   /** @private */
   selectDownloadLocation_: function() {
     chrome.send('selectDownloadLocation');
   },
 
 // <if expr="chromeos">
   /**
    * @param {string} path
    * @return {string} The download location string that is suitable to display
    *     in the UI.
    * @private
    */
   getDownloadLocation_: function(path) {
     // Replace /special/drive-<hash>/root with "Google Drive" for remote files,
     // /home/chronos/user/Downloads or /home/chronos/u-<hash>/Downloads with
     // "Downloads" for local paths, and '/' with ' \u203a ' (angled quote sign)
     // everywhere. It is used only for display purpose.
     path = path.replace(/^\/special\/drive[^\/]*\/root/, 'Google Drive');
     path = path.replace(/^\/home\/chronos\/(user|u-[^\/]*)\//, '');
     path = path.replace(/\//g, ' \u203a ');
     return path;
   },
 // </if>
 });