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 23 matching lines @@
       type: Boolean,
       value: false,
       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_: {

[tsergeant, 2016/04/18 01:26:36]

Nit: Rename this to `searching` with no underscore to show that it's a public
property.

(In javascript, we use an underscore at the end of a name to mark a method or
property as private).

[lshang, 2016/04/22 01:25:03]

Done.

+      type: Boolean,
+      value: false
     }
   },
 
   /**
    * Changes the toolbar background color depending on whether any history items
    * are currently selected.
    * @private
    */
   changeToolbarView_: function() {
     this.itemsSelected_ = this.count > 0;
@@ skipping 51 matching lines @@
    * @private
    */
   deletingAllowed_: function() {
     return loadTimeData.getBoolean('allowDeletingHistory');
   },
 
   numberOfItemsSelected_: function(count) {
     return count > 0 ? loadTimeData.getStringF('itemsSelected', count) : '';
   }
 });