MD WebUI: Reduce flickering of spinner in toolbar search field

ui/webui/resources/cr_elements/cr_toolbar/cr_toolbar_search_field.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-search-field',
 
   behaviors: [CrSearchFieldBehavior],
 
   properties: {
@@ skipping 76 matching lines @@
    */
   computeIconAriaHidden_: function(narrow) {
     return Boolean(!narrow).toString();
   },
 
   /**
    * @return {boolean}
    * @private
    */
   computeIsSpinnerShown_: function() {
-    return this.spinnerActive && this.showingSearch;
+    var showSpinner = this.spinnerActive && this.showingSearch;
+    if (showSpinner)
+      this.$.spinnerTemplate.if = true;
+    return showSpinner;
   },
 
   /** @private */
   onInputFocus_: function() {
     this.searchFocused_ = true;
   },
 
   /** @private */
   onInputBlur_: function() {
     this.searchFocused_ = false;
@@ skipping 37 matching lines @@
 
     if (this.showingSearch) {
       this.focus_();
       return;
     }
 
     this.setValue('');
     this.getSearchInput().blur();
   },
 });