Have StyleSheetCollections constructor take a Document reference in argument

Source/core/dom/shadow/ShadowRoot.h

 /*
  * Copyright (C) 2011 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 154 matching lines @@
 {
     ASSERT_WITH_SECURITY_IMPLICATION(!treeScope || (treeScope->rootNode() && treeScope->rootNode()->isShadowRoot()));
     return static_cast<const ShadowRoot*>(treeScope);
 }
 
 inline ShadowRoot* toShadowRoot(TreeScope* treeScope)
 {
     return const_cast<ShadowRoot*>(toShadowRoot(static_cast<const TreeScope*>(treeScope)));
 }
 
+inline ShadowRoot& toShadowRoot(TreeScope& treeScope)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(treeScope.rootNode() && treeScope.rootNode()->isShadowRoot());
+    return static_cast<ShadowRoot&>(treeScope);
+}
+
 } // namespace
 
 #endif