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

ui/webui/resources/cr_elements/cr_action_menu/cr_action_menu.js

Index: ui/webui/resources/cr_elements/cr_action_menu/cr_action_menu.js
diff --git a/ui/webui/resources/cr_elements/cr_action_menu/cr_action_menu.js b/ui/webui/resources/cr_elements/cr_action_menu/cr_action_menu.js
index 9f58dc4f6cd9079f59c2ee05364b0f1f5aef5e46..7e36605b666059e12d6a4be162b791ca6d363935 100644
--- a/ui/webui/resources/cr_elements/cr_action_menu/cr_action_menu.js
+++ b/ui/webui/resources/cr_elements/cr_action_menu/cr_action_menu.js
@@ -26,12 +26,16 @@ Polymer({
    */
   boundClose_: null,
 
+  /** @private {boolean} */
+  hasMousemoveListener_: false,
+
   hostAttributes: {
     tabindex: 0,
   },
 
   listeners: {
     'keydown': 'onKeyDown_',
+    'mouseover': 'onMouseover_',
     'tap': 'onTap_',
   },
 
@@ -73,6 +77,14 @@ Polymer({
       return;
     }
 
+    if (!this.hasMousemoveListener_) {

[dpapad, 2017/04/06 18:00:31]

Does this need to be above the following check? Can we move it below that
instead?

if (e.key !== 'ArrowDown' && e.key !== 'ArrowUp')
  return;

[scottchen, 2017/04/06 21:40:23]

Acknowledged. I moved it into the if(nextOption) statement, so that a listener
is attached only when we're about to move the focus().

+      this.hasMousemoveListener_ = true;
+      listenOnce(this, 'mousemove', function(e) {
+        this.onMouseover_(e);
+        this.hasMousemoveListener_ = false;
+      }.bind(this));
+    }
+
     if (e.key !== 'ArrowDown' && e.key !== 'ArrowUp')
       return;
 
@@ -84,6 +96,26 @@ Polymer({
   },
 
   /**
+   * @param {!Event} e
+   * @private
+   */
+  onMouseover_: function(e) {
+    // TODO(scottchen): Using "focus" to determine selected item might mess
+    // with screen readers in some edge cases.
+    var i = 0;
+    do {
+      var target = e.path[i++];
+      if (target.classList && target.classList.contains('dropdown-item')) {
+        target.focus();
+        return;
+      }
+    } while (this != target);
+
+    // The user moved the mouse off the options. Reset focus to the dialog.
+    this.focus();
+  },
+
+  /**
    * @param {number} step -1 for getting previous option (up), 1 for getting
    *     next option (down).
    * @return {?Element} The next focusable option, taking into account