[VR Shell] Fix hidden elements being hit-testable.

chrome/browser/resources/vr_shell/vr_shell_ui.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.
 
 var vrShellUi = (function() {
   'use strict';
 
   let ui = new scene.Scene();
   let uiManager;
   let nativeCommandHandler;
@@ skipping 33 matching lines @@
       this.fullscreen = false;
 
       let element = new api.UiElement(0, 0, 0, 0);
       element.setFill(new api.Content());
       element.setVisible(false);
       element.setSize(
           this.SCREEN_HEIGHT * this.SCREEN_RATIO, this.SCREEN_HEIGHT);
       element.setTranslation(0, 0, -this.BROWSING_SCREEN_DISTANCE);
       this.elementId = ui.addElement(element);
 
-      // Place an invisible but hittable plane behind the content quad, to keep
-      // the reticle roughly planar with the content if near content.
+      // Place an invisible (fill none) but hittable plane behind the content
+      // quad, to keep the reticle roughly planar with the content if near
+      // content.
       let backPlane = new api.UiElement(0, 0, 0, 0);
-      backPlane.setVisible(false);
-      backPlane.setHitTestable(true);
       backPlane.setSize(1000, 1000);
       backPlane.setTranslation(0, 0, -0.01);
       backPlane.setParentId(this.elementId);
+      backPlane.setFill(new api.NoFill());
       ui.addElement(backPlane);
 
       this.updateState();
     }
 
     setEnabled(enabled) {
       let update = new api.UiElementUpdate();
       update.setVisible(enabled);
       ui.updateElement(this.elementId, update);
       if (enabled) {
@@ skipping 896 matching lines @@
     nativeCommandHandler.handleCommand(dict);
   }
 
   return {
     initialize: initialize,
     command: command,
   };
 })();
 
 window.addEventListener('load', vrShellUi.initialize);