MD History: Add spinners when new data is loading or searching

chrome/browser/resources/md_history/history_toolbar.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.
 
 /**
  * @constructor
  * @implements {SearchFieldDelegate}
  * @param {!HistoryToolbarElement} toolbar This history-toolbar.
  */
 function ToolbarSearchFieldDelegate(toolbar) {
@@ skipping 25 matching lines @@
       reflectToAttribute: true
     },
 
     // The most recent term entered in the search field. Updated incrementally
     // as the user types.
     searchTerm: {
       type: String,
       value: ''
     },
 
+    // True if it's searching at the backend.
+    searching: {
+      type: Boolean,
+      value: false
+    },
+
     // True if the page has a sidebar that we need to account for when
     // positioning toolbar items.
     hasSidebar: {
       type: Boolean,
       value: false,
       reflectToAttribute: true
     }
   },
 
   /**
@@ skipping 57 matching lines @@
    * @private
    */
   deletingAllowed_: function() {
     return loadTimeData.getBoolean('allowDeletingHistory');
   },
 
   numberOfItemsSelected_: function(count) {
     return count > 0 ? loadTimeData.getStringF('itemsSelected', count) : '';
   }
 });