MD WebUI: Change <cr-toolbar> clear button to not close the 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.
 
 // TODO(tsergeant): Add tests for cr-toolbar-search-field.
 Polymer({
   is: 'cr-toolbar-search-field',
 
   behaviors: [CrSearchFieldBehavior],
 
@@ skipping 82 matching lines @@
    */
   showSearch_: function(e) {
     if (e.target != this.$.clearSearch)
       this.showingSearch = true;
   },
 
   /**
    * @param {Event} e
    * @private
    */
-  hideSearch_: function(e) {
-    this.showingSearch = false;
-    e.stopPropagation();
+  clearSearch_: function(e) {
+    this.setValue('');
+    this.getSearchInput().focus();
   }
 });