WebUI: Return focus to anchor element when cr-action-menu is closed.

ui/webui/resources/cr_elements/cr_action_menu/cr_action_menu.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: 'cr-action-menu',
   extends: 'dialog',
 
   /**
    * List of all options in this action menu.
    * @private {?NodeList<!Element>}
    */
   options_: null,
 
   /**
+   * The element which the action menu will be anchored to. Also the element
+   * where focus will be returned after the menu is closed.
+   * @private {?Element}
+   */
+  anchorElement_: null,
+
+  /**
    * Reference to the bound window's resize listener, such that it can be
    * removed on detach.
    * @private {?Function}
    */
   onWindowResize_: null,
 
   hostAttributes: {
     tabindex: 0,
   },
 
@@ skipping 26 matching lines @@
       this.close();
       e.stopPropagation();
     }
   },
 
   /**
    * @param {!KeyboardEvent} e
    * @private
    */
   onKeyDown_: function(e) {
-    if (e.key == 'Tab') {
+    if (e.key == 'Tab' || e.key == 'Escape') {
       this.close();
+      e.preventDefault();
       return;
     }
 
     if (e.key !== 'ArrowDown' && e.key !== 'ArrowUp')
       return;
 
     var nextOption = this.getNextOption_(e.key == 'ArrowDown' ? 1 : - 1);
     if (nextOption)
       nextOption.focus();
 
@@ skipping 25 matching lines @@
     } while (!nextOption && counter < numOptions);
 
     return nextOption;
   },
 
   /** @override */
   close: function() {
     // Removing 'resize' listener when dialog is closed.
     this.removeResizeListener_();
     HTMLDialogElement.prototype.close.call(this);
+    this.anchorElement_.focus();
+    this.anchorElement_ = null;
   },
 
   /**
    * Shows the menu anchored to the given element.
    * @param {!Element} anchorElement
    */
   showAt: function(anchorElement) {
+    this.anchorElement_ = anchorElement;
     this.onWindowResize_ = this.onWindowResize_ || function() {
       if (this.open)
         this.close();
     }.bind(this);
     window.addEventListener('resize', this.onWindowResize_);
 
     this.showModal();
 
-    var rect = anchorElement.getBoundingClientRect();
-    if (getComputedStyle(anchorElement).direction == 'rtl') {
+    var rect = this.anchorElement_.getBoundingClientRect();
+    if (getComputedStyle(this.anchorElement_).direction == 'rtl') {
       var right = window.innerWidth - rect.left - this.offsetWidth;
       this.style.right = right + 'px';
     } else {
       var left = rect.right - this.offsetWidth;
       this.style.left = left + 'px';
     }
 
     // Attempt to show the menu starting from the top of the rectangle and
     // extending downwards. If that does not fit within the window, fallback to
     // starting from the bottom and extending upwards.
     var top = rect.top + this.offsetHeight <= window.innerHeight ?
         rect.top :
         rect.bottom - this.offsetHeight - Math.max(
             rect.bottom - window.innerHeight, 0);
 
     this.style.top = top + 'px';
   },
 });