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..1db658c94145dd1b8139b106e457e659cf9125c9 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
@@ -32,6 +32,7 @@ Polymer({
 
   listeners: {
     'keydown': 'onKeyDown_',
+    'mouseover': 'onMouseover_',
     'tap': 'onTap_',
   },
 
@@ -73,6 +74,8 @@ Polymer({
       return;
     }
 
+    listenOnce(this, 'mousemove', this.onMouseover_.bind(this));

[dpapad, 2017/04/06 00:06:02]

We are leaking mousemove listeners. When the user presses for example down,
down, down, we are registering 3 of them, but none of them has fired yet. When
the user finally moves their mouse, instead of getting one invocation, we get 3
of them. We need to only add a listener if we haven't added one already.

[Dan Beam, 2017/04/06 00:08:35]

sure, that makes sense

[scottchen, 2017/04/06 00:44:33]

Done.

+
     if (e.key !== 'ArrowDown' && e.key !== 'ArrowUp')
       return;
 
@@ -84,6 +87,25 @@ Polymer({
   },
 
   /**
+   * @param {!MouseEvent} e
+   * @private
+   */
+  onMouseover_: function(e) {
+    // TODO(scottchen): Using "focus" to determine selected item might mess
+    // with screen readers in some edge cases.
+    var target = e.path[0];
+    for (var i = 0; this != target; target = e.path[i++]) {

[Dan Beam, 2017/04/05 23:42:30]

nit:

var i = 0;
for (var target; this != target; target = e.path[i++]) {
  ...
}

[scottchen, 2017/04/06 00:44:33]

I changed it to a do-while for readability.

+      if (target.classList && target.classList.contains('dropdown-item')) {
+        target.focus();
+        return;
+      }
+    };
+
+    // 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