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..05346b3e73c10a95b04d027ddccfd0fd84598a1a 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_',
+    'mousemove': 'onMouseMove_',
     'tap': 'onTap_',
   },
 
@@ -83,6 +84,27 @@ Polymer({
     e.preventDefault();
   },
 
+  debounceFlusher_: null,
+
+  onMouseMove_: function(e) {
+    var target = e.target;
+
+    if (!this.debounceFlusher_) {
+      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();
+      else
+        this.focus();  // Blur option focus but keep up/down button working.
+    }.bind(this), 10);
+  },
+
   /**
    * @param {number} step -1 for getting previous option (up), 1 for getting
    *     next option (down).
@@ -99,6 +121,10 @@ Polymer({
     var focusedIndex =
         Array.prototype.indexOf.call(this.options_, this.root.activeElement);
 
+    // Avoid off-by-one when nothing is focused and up is pressed.
+    if (focusedIndex === -1 && step === -1)
+      focusedIndex = 0;
+
     do {
       focusedIndex = (numOptions + focusedIndex + step) % numOptions;
       nextOption = this.options_[focusedIndex];