MD WebUI: Use arrow keys for navigation in cr-shared-menu, close on tab

ui/webui/resources/cr_elements/cr_shared_menu/cr_shared_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.
 
 /** Same as paper-menu-button's custom easing cubic-bezier param. */
 var SLIDE_CUBIC_BEZIER = 'cubic-bezier(0.3, 0.95, 0.5, 1)';
 
 Polymer({
   is: 'cr-shared-menu',
 
-  behaviors: [Polymer.IronA11yKeysBehavior],
-
   properties: {
     menuOpen: {
       type: Boolean,
       observer: 'menuOpenChanged_',
       value: false,
       notify: true,
     },
 
     /**
      * The contextual item that this menu was clicked for, e.g. the data used to
@@ skipping 46 matching lines @@
         return [{
           name: 'fade-out-animation',
           timing: {
             duration: 150
           }
         }];
       }
     }
   },
 
-  keyBindings: {
-    'tab': 'onTabPressed_',
-  },
-
   listeners: {
     'dropdown.iron-overlay-canceled': 'onOverlayCanceled_',
   },
 
   /**
    * The last anchor that was used to open a menu. It's necessary for toggling.
    * @private {?Element}
    */
   lastAnchor_: null,
 
-  /**
-   * The first focusable child in the menu's light DOM.
-   * @private {?Element}
-   */
-  firstFocus_: null,
-
-  /**
-   * The last focusable child in the menu's light DOM.
-   * @private {?Element}
-   */
-  lastFocus_: null,
-
   /** @override */
   attached: function() {
     window.addEventListener('resize', this.closeMenu.bind(this));
+    this.$.menu.addEventListener(
+        'keydown', this.onCaptureKeyDown_.bind(this), true);
   },
 
   /** Closes the menu. */
   closeMenu: function() {
     if (this.root.activeElement == null) {
       // Something else has taken focus away from the menu. Do not attempt to
       // restore focus to the button which opened the menu.
       this.$.dropdown.restoreFocusOnClose = false;
     }
     this.menuOpen = false;
   },
 
   /**
    * Opens the menu at the anchor location.
    * @param {!Element} anchor The location to display the menu.
    * @param {!Object=} opt_itemData The contextual item's data.
    */
   openMenu: function(anchor, opt_itemData) {
     if (this.lastAnchor_ == anchor && this.menuOpen)
       return;
 
     if (this.menuOpen)
       this.closeMenu();
 
     this.itemData = opt_itemData || null;
     this.lastAnchor_ = anchor;
     this.$.dropdown.restoreFocusOnClose = true;
-
-    var focusableChildren = Polymer.dom(this).querySelectorAll(
-        '[tabindex]:not([disabled]):not([hidden]),' +
-        'button:not([disabled]):not([hidden])');
-    if (focusableChildren.length > 0) {
-      this.$.dropdown.focusTarget = focusableChildren[0];
-      this.firstFocus_ = focusableChildren[0];
-      this.lastFocus_ = focusableChildren[focusableChildren.length - 1];
-    }
+    this.$.menu.selected = -1;
 
     // Move the menu to the anchor.
     this.$.dropdown.positionTarget = anchor;
     this.menuOpen = true;
   },
 
   /**
    * Toggles the menu for the anchor that is passed in.
    * @param {!Element} anchor The location to display the menu.
    * @param {!Object=} opt_itemData The contextual item's data.
    */
   toggleMenu: function(anchor, opt_itemData) {
     if (anchor == this.lastAnchor_ && this.menuOpen)
       this.closeMenu();
     else
       this.openMenu(anchor, opt_itemData);
   },
 
   /**
-   * Trap focus inside the menu. As a very basic heuristic, will wrap focus from
-   * the first element with a nonzero tabindex to the last such element.
-   * TODO(tsergeant): Use iron-focus-wrap-behavior once it is available
-   * (https://github.com/PolymerElements/iron-overlay-behavior/issues/179).
-   * @param {CustomEvent} e
+   * Close the menu when tab is pressed. Note that we must
+   * explicitly add a capture event listener to do this as iron-menu-behavior
+   * eats all key events during bubbling. See
+   * https://github.com/PolymerElements/iron-menu-behavior/issues/56.
+   * This will move focus to the next focusable element before/after the
+   * anchor.
+   * @private
    */
-  onTabPressed_: function(e) {
-    if (!this.firstFocus_ || !this.lastFocus_)
-      return;
-
-    var toFocus;
-    var keyEvent = e.detail.keyboardEvent;
-    if (keyEvent.shiftKey && keyEvent.target == this.firstFocus_)
-      toFocus = this.lastFocus_;
-    else if (!keyEvent.shiftKey && keyEvent.target == this.lastFocus_)
-      toFocus = this.firstFocus_;
-
-    if (!toFocus)
-      return;
-
-    e.preventDefault();
-    toFocus.focus();
+  onCaptureKeyDown_: function(e) {
+    if (Polymer.IronA11yKeysBehavior.keyboardEventMatchesKeys(e, 'tab')) {

[Dan Beam, 2016/09/23 06:25:32]

what does this do on shift tab?

[tsergeant, 2016/09/26 01:51:01]

The conditional matches on shift tab, so the menu will close and focus will move
back to the previous element.

+      // Need to refocus the anchor synchronously so that the tab event takes
+      // effect on it.
+      this.$.dropdown.restoreFocusOnClose = false;
+      this.lastAnchor_.focus();
+      this.closeMenu();
+    }
   },
 
   /**
    * Ensure the menu is reset properly when it is closed by the dropdown (eg,
    * clicking outside).
    * @private
    */
   menuOpenChanged_: function() {
     if (!this.menuOpen) {
       this.itemData = null;
       this.lastAnchor_ = null;
     }
   },
 
   /**
    * Prevent focus restoring when tapping outside the menu. This stops the
    * focus moving around unexpectedly when closing the menu with the mouse.
    * @param {CustomEvent} e
    * @private
    */
   onOverlayCanceled_: function(e) {
     if (e.detail.type == 'tap')
       this.$.dropdown.restoreFocusOnClose = false;
   },
 });