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

ui/webui/resources/cr_elements/cr_toolbar/cr_toolbar.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: 'cr-toolbar',
 
   properties: {
+    // Name to display in the toolbar, in titlecase.
+    pageName: String,
+
+    // Prompt text to display in the search field.
+    searchPrompt: String,
+
+    // Tooltip to display on the clear search button.
+    clearLabel: String,
+
+    // Value is proxied through to cr-toolbar-search-field. When true,
+    // the search field will show a processing spinner.
+    spinnerActive: Boolean,
+
     /** @private */
     narrow_: {
       type: Boolean,
       reflectToAttribute: true
     },
 
     /** @private */
     showingSearch_: {
       type: Boolean,
       reflectToAttribute: true,
     },
-
-    // Name to display in the toolbar, in titlecase.
-    pageName: String,
-
-    // Prompt text to display in the search field.
-    searchPrompt: String,
-
-    // Tooltip to display on the clear search button.
-    clearLabel: String,
   },
 
   /** @return {!CrToolbarSearchFieldElement} */
   getSearchField: function() {
     return this.$.search;
   }
 });