MD History: Convert synced device collapse icon to a button

chrome/browser/resources/md_history/synced_device_card.js

 // Copyright 2016 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.
 
 Polymer({
   is: 'history-synced-device-card',
 
   properties: {
     // Name of the synced device.
     device: {type: String, value: ''},
@@ skipping 69 matching lines @@
       for (var i = 0; i < this.tabs.length; i++) {
         icons[i].style.backgroundImage =
             cr.icon.getFaviconImageSet(this.tabs[i].url);
       }
     });
   },
 
   /** @private */
   isWindowSeparatorIndex_: function(index, separatorIndexes) {
     return this.separatorIndexes.indexOf(index) != -1;
-  }
+  },
+
+  /**
+   * @param {boolean} cardOpen
+   * @return {string}
+   */
+  getCollapseTitle_: function(cardOpen) {
+    return cardOpen ? loadTimeData.getString('collapseSessionButton') :
+                      loadTimeData.getString('expandSessionButton');
+  },
 });