[MD Bookmarks] Remove the bookmarks-sidebar element.

chrome/test/data/webui/md_bookmarks/app_test.js

 // Copyright 2017 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.
 
 suite('<bookmarks-app>', function() {
   var app;
   var store;
 
   function resetStore() {
     store = new bookmarks.TestStore({});
@@ skipping 38 matching lines @@
     resetStore();
     app = document.createElement('bookmarks-app');
     replaceBody(app);
 
     // Ensure closed folders are read from local storage.
     assertDeepEquals(closedFoldersList, normalizeSet(store.data.closedFolders));
   });
 
   test('write and load sidebar width', function() {
     assertEquals(
-        app.$.sidebar.getComputedStyleValue('width'), app.sidebarWidth_);
+        getComputedStyle(app.$.sidebar).width, app.sidebarWidth_);
 
     var sidebarWidth = '500px';
     app.$.sidebar.style.width = sidebarWidth;
     cr.dispatchSimpleEvent(app.$.splitter, 'resize');
     assertEquals(
         sidebarWidth, window.localStorage[LOCAL_STORAGE_TREE_WIDTH_KEY]);
 
     app = document.createElement('bookmarks-app');
     replaceBody(app);
 
     assertEquals(sidebarWidth, app.$.sidebar.style.width);
   });
 });