ShadowRoot should have a host property.

Source/core/dom/shadow/ShadowRoot.idl

 /*
  * Copyright (C) 2012 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Neither the name of Google Inc. nor the names of its
@@ skipping 28 matching lines @@
     Element getElementById([Default=Undefined] optional DOMString elementId);
     NodeList getElementsByClassName([Default=Undefined] optional DOMString className);
     NodeList getElementsByTagName([Default=Undefined] optional DOMString tagName);
     NodeList getElementsByTagNameNS([TreatNullAs=NullString,Default=Undefined] optional DOMString namespaceURI,
                                     [Default=Undefined] optional DOMString localName);
 
     Element elementFromPoint([Default=Undefined] optional long x,
                              [Default=Undefined] optional long y);
 
     [RuntimeEnabled=ShadowDOM] readonly attribute StyleSheetList styleSheets;
+    [RuntimeEnabled=ShadowDOM] readonly attribute Element host;
 };