MD Settings: mouse movements should focus cr-action-menu items

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.
@@ skipping 14 matching lines @@
    * @private {?Function}
    */
   boundClose_: null,
 
   hostAttributes: {
     tabindex: 0,
   },
 
   listeners: {
     'keydown': 'onKeyDown_',
+    'mousemove': 'onMouseMove_',
     'tap': 'onTap_',
   },
 
   /** override */
   attached: function() {
     this.options_ = this.querySelectorAll('.dropdown-item');
   },
 
   /** override */
   detached: function() {
@@ skipping 31 matching lines @@
     if (e.key !== 'ArrowDown' && e.key !== 'ArrowUp')
       return;
 
     var nextOption = this.getNextOption_(e.key == 'ArrowDown' ? 1 : -1);
     if (nextOption)
       nextOption.focus();
 
     e.preventDefault();
   },
 
+  debounceFlusher_: null,
+
+  onMouseMove_: function(e) {
+    var target = e.target;
+
+    if(!this.debounceFlusher_) {

[scottchen, 2017/04/04 20:43:12]

Need this, otherwise if the user keeps moving their mouse on the menu non-stop,
the hover will never change target.

+      this.debounceFlusher_ = setTimeout(function(){
+        this.flushDebouncer('cr-action-menu-mousemove');
+        this.debounceFlusher_ = null;
+      }.bind(this), 10);
+    }
+
+    this.debounce('cr-action-menu-mousemove', function(){
+      if(target.classList.contains('dropdown-item') && 
+          target != document.activeElement)
+        target.focus();
+    }.bind(this), 10);
+  },
+
   /**
    * @param {number} step -1 for getting previous option (up), 1 for getting
    *     next option (down).
    * @return {?Element} The next focusable option, taking into account
    *     disabled/hidden attributes, or null if no focusable option exists.
    * @private
    */
   getNextOption_: function(step) {
     // Using a counter to ensure no infinite loop occurs if all elements are
     // hidden/disabled.
@@ skipping 55 matching lines @@
     // 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';
   },
 });