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

chrome/browser/resources/md_bookmarks/mouse_focus_behavior.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.
 
 cr.define('bookmarks', function() {
+  /** @const */
+  var MOUSE_FOCUS_CLASS = 'mouse-focus';
+
   /**
    * Behavior which adds the 'mouse-focus' class to a target element when it
    * gains focus from the mouse, allowing the outline to be hidden without
    * affecting keyboard users.
    * @polymerBehavior
    */
   var MouseFocusBehavior = {
     attached: function() {
       this.boundOnMousedown_ = this.onMousedown_.bind(this);
       this.boundClearMouseFocus_ = this.clearMouseFocus.bind(this);
 
       var target = this.getFocusTarget();
       target.addEventListener('mousedown', this.boundOnMousedown_);
+      target.addEventListener('contextmenu', this.boundOnMousedown_);
       target.addEventListener('blur', this.boundClearMouseFocus_);
     },
 
     detached: function() {
       var target = this.getFocusTarget();
       target.removeEventListener('mousedown', this.boundOnMousedown_);
+      target.removeEventListener('contextmenu', this.boundOnMousedown_);
       target.removeEventListener('blur', this.boundClearMouseFocus_);
     },
 
     /**
      * Returns the element that should be watched for focus changes. Clients
      * can override, but it is assumed that the return value is constant over
      * the lifetime of the element.
      * @return {!HTMLElement}
      */
     getFocusTarget: function() {
       return this;
     },
 
     /** Reset the focus state when focus leaves the target element. */
     clearMouseFocus: function() {
-      this.getFocusTarget().classList.remove('mouse-focus');
+      this.getFocusTarget().classList.remove(MOUSE_FOCUS_CLASS);
     },
 
     /** @private */
     onMousedown_: function() {
-      this.getFocusTarget().classList.add('mouse-focus');
+      this.addMouseFocusClass(this.getFocusTarget());
+    },
+
+    /**
+     * @param {HTMLElement} element
+     * @return {boolean}
+     */
+    isMouseFocused: function(element) {
+      return element.classList.contains(MOUSE_FOCUS_CLASS);
+    },
+
+    /** @param {HTMLElement} element */
+    addMouseFocusClass: function(element) {
+      element.classList.add(MOUSE_FOCUS_CLASS);
     },
   };
 
   return {
     MouseFocusBehavior: MouseFocusBehavior,
   };
 });