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

Source/core/html/HTMLMediaElement.cpp

Index: Source/core/html/HTMLMediaElement.cpp
diff --git a/Source/core/html/HTMLMediaElement.cpp b/Source/core/html/HTMLMediaElement.cpp
index 91f87f6d7aef089312dd1dd65cbea2124e420c4d..5a413b76a92dd59e447c11ba062f168869783f8c 100644
--- a/Source/core/html/HTMLMediaElement.cpp
+++ b/Source/core/html/HTMLMediaElement.cpp
@@ -300,9 +300,6 @@ HTMLMediaElement::HTMLMediaElement(const QualifiedName& tagName, Document& docum
     if (document.settings() && document.settings()->mediaPlaybackRequiresUserGesture())
         m_userGestureRequiredForPlay = true;
 
-    // We must always have a ShadowRoot so children like <source> will not render
-    // as they never have an insertion point.
-    ensureUserAgentShadowRoot();
     setHasCustomStyleCallbacks();
     addElementToDocumentMap(this, &document);
 }