Don't mutate the DOM from inside an Element's constructor

Source/core/html/HTMLVideoElement.cpp

 /*
  * Copyright (C) 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 14 matching lines @@
 
 #include "config.h"
 #include "core/html/HTMLVideoElement.h"
 
 #include "CSSPropertyNames.h"
 #include "HTMLNames.h"
 #include "bindings/v8/ExceptionState.h"
 #include "core/dom/Attribute.h"
 #include "core/dom/Document.h"
 #include "core/dom/ExceptionCode.h"
+#include "core/dom/shadow/ShadowRoot.h"
+#include "core/frame/Settings.h"
 #include "core/html/HTMLImageLoader.h"
 #include "core/html/canvas/CanvasRenderingContext.h"
 #include "core/html/parser/HTMLParserIdioms.h"
-#include "core/frame/Settings.h"
 #include "core/rendering/RenderImage.h"
 #include "core/rendering/RenderVideo.h"
 #include "platform/UserGestureIndicator.h"
 
 namespace WebCore {
 
 using namespace HTMLNames;
 
 inline HTMLVideoElement::HTMLVideoElement(Document& document)
     : HTMLMediaElement(videoTag, document)
 {
     ScriptWrappable::init(this);
     if (document.settings())
         m_defaultPosterURL = AtomicString(document.settings()->defaultVideoPosterURL());
 }
 
 PassRefPtrWillBeRawPtr<HTMLVideoElement> HTMLVideoElement::create(Document& document)
 {
-    RefPtrWillBeRawPtr<HTMLVideoElement> videoElement(adoptRefWillBeRefCountedGarbageCollected(new HTMLVideoElement(document)));
-    videoElement->suspendIfNeeded();
-    return videoElement.release();
+    RefPtrWillBeRawPtr<HTMLVideoElement> video = adoptRefWillBeRefCountedGarbageCollected(new HTMLVideoElement(document));
+    video->ensureUserAgentShadowRoot();
+    video->suspendIfNeeded();
+    return video.release();
 }
 
 bool HTMLVideoElement::rendererIsNeeded(const RenderStyle& style)
 {
     return HTMLElement::rendererIsNeeded(style);
 }
 
 RenderObject* HTMLVideoElement::createRenderer(RenderStyle*)
 {
     return new RenderVideo(this);
@@ skipping 229 matching lines @@
 {
     return !hasSingleSecurityOrigin() || (!(webMediaPlayer() && webMediaPlayer()->didPassCORSAccessCheck()) && destinationSecurityOrigin->taintsCanvas(currentSrc()));
 }
 
 FloatSize HTMLVideoElement::sourceSize() const
 {
     return FloatSize(videoWidth(), videoHeight());
 }
 
 }