[MD Bookmarks] Fix sidebar issues.

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({});
     store.acceptInitOnce();
     bookmarks.Store.instance_ = store;
 
     chrome.bookmarks.getTree = function(fn) {
       fn([
         createFolder(
             '0',
             [
               createFolder(
                   '1',
                   [
                     createFolder('11', []),
                   ]),
             ]),
       ]);
     };
   }
 
   setup(function() {
+    window.localStorage.clear();
     resetStore();
 
     app = document.createElement('bookmarks-app');
     replaceBody(app);
   });
 
-  teardown(function() {
-    window.localStorage.clear();
-  });
 
   test('write and load closed folder state', function() {
     var closedFoldersList = ['1'];
     var closedFolders = new Set(closedFoldersList);
     store.data.closedFolders = closedFolders;
     store.notifyObservers();
 
     // Ensure closed folders are written to local storage.
     assertDeepEquals(
         JSON.stringify(Array.from(closedFolders)),
         window.localStorage[LOCAL_STORAGE_CLOSED_FOLDERS_KEY]);
 
     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.$.sidebar.getComputedStyleValue('width'), app.sidebarWidth_);
+
+    var sidebarWidth = '500px';
+    app.$.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);
+  });
 });