MD WebUI: Add loading spinner to cr-toolbar, hook into MD History toolbar

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,
       notify: true,
     },
 
-    // True if waiting on the search backend.
-    searching: {
+    // True if the backend is processing and a spinner should be shown in the
+    // toolbar.
+    spinnerActive: {
       type: Boolean,
       value: false
     },
 
     // Whether domain-grouped history is enabled.
     isGroupedMode: {
       type: Boolean,
       reflectToAttribute: true,
     },
 
@@ skipping 70 matching lines @@
   numberOfItemsSelected_: function(count) {
     return count > 0 ? loadTimeData.getStringF('itemsSelected', count) : '';
   },
 
   getHistoryInterval_: function(queryStartTime, queryEndTime) {
     // TODO(calamity): Fix the format of these dates.
     return loadTimeData.getStringF(
       'historyInterval', queryStartTime, queryEndTime);
   }
 });