UA shadow root of <marquee> should not be exposed to user scripts

Source/core/html/HTMLMarqueeElement.js

 // Copyright 2014 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.
 
 'use strict';
 
 installClass('HTMLMarqueeElement', function(HTMLMarqueeElementPrototype) {
 
     var kDefaultScrollAmount = 6;
     var kDefaultScrollDelayMS = 85;
@@ skipping 73 matching lines @@
     reflectAttribute(HTMLMarqueeElementPrototype, 'behavior', 'behavior');
     reflectAttribute(HTMLMarqueeElementPrototype, 'bgcolor', 'bgColor');
     reflectAttribute(HTMLMarqueeElementPrototype, 'direction', 'direction');
     reflectAttribute(HTMLMarqueeElementPrototype, 'height', 'height');
     reflectAttribute(HTMLMarqueeElementPrototype, 'hspace', 'hspace');
     reflectAttribute(HTMLMarqueeElementPrototype, 'vspace', 'vspace');
     reflectAttribute(HTMLMarqueeElementPrototype, 'width', 'width');
     reflectBooleanAttribute(HTMLMarqueeElementPrototype, 'truespeed', 'trueSpeed');
 
     HTMLMarqueeElementPrototype.createdCallback = function() {
-        var shadow = this.createShadowRoot();
+        var shadow = this.createUserAgentShadowRoot();
         var style = document.createElement('style');
         style.textContent = ':host { display: inline-block; width: -webkit-fill-available; overflow: hidden; text-align: initial; }'
             + ':host([direction="up"]), :host([direction="down"]) { overflow: initial; overflow-y: hidden; }';
         shadow.appendChild(style);
 
         var mover = document.createElement('div');
         shadow.appendChild(mover);
 
         mover.appendChild(document.createElement('content'));
 
@@ skipping 283 matching lines @@
             cancelAnimationFrame(this.continueCallback_);
             this.continueCallback_ = null;
             return;
         }
 
         if (this.player_) {
             this.player_.pause();
         }
     };
 });