[MD Bookmarks] Restore focus after closing a dialog or context menu.

chrome/browser/resources/md_bookmarks/item.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: 'bookmarks-item',
 
   behaviors: [
     bookmarks.MouseFocusBehavior,
     bookmarks.StoreClient,
@@ skipping 49 matching lines @@
   getDropTarget: function() {
     return this;
   },
 
   /**
    * @param {Event} e
    * @private
    */
   onContextMenu_: function(e) {
     e.preventDefault();
+    this.focus();
     if (!this.isSelectedItem_)
       this.selectThisItem_();
 
     this.fire('open-item-menu', {
       x: e.clientX,
       y: e.clientY,
     });
   },
 
   /**
@@ skipping 69 matching lines @@
   },
 
   /**
    * @param {string} url
    * @private
    */
   updateFavicon_: function(url) {
     this.$.icon.style.backgroundImage = cr.icon.getFavicon(url);
   },
 });