[MD History] Refactor history.html into a history-app element.

chrome/test/data/webui/md_history/history_toolbar_test.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.
 
 cr.define('md_history.history_toolbar_test', function() {
   function registerTests() {
     suite('history-toolbar', function() {
       var element;
       var toolbar;
       var TEST_HISTORY_RESULTS;
 
       suiteSetup(function() {
-        element = $('history-list');
-        toolbar = $('toolbar');
+        element = $('history-app').$['history-list'];
+        toolbar = $('history-app').$['toolbar'];
         TEST_HISTORY_RESULTS =
             [createHistoryEntry('2016-03-15', 'https://google.com')];
       });
 
       test('selecting checkbox causes toolbar to change', function(done) {
         element.addNewResults(TEST_HISTORY_RESULTS, '');
 
         flush(function() {
           var item = element.$$('history-item');
           MockInteractions.tap(item.$.checkbox);
@@ skipping 44 matching lines @@
         element.historyData = [];
         registerMessageCallback('queryHistory', this, undefined);
         toolbar.count = 0;
       });
     });
   }
   return {
     registerTests: registerTests
   };
 });