Oilpan: Prepare moving ShadowRoot to oilpan.

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 37 matching lines @@
 public:
     // FIXME: We will support multiple shadow subtrees, however current implementation does not work well
     // if a shadow root is dynamically created. So we prohibit multiple shadow subtrees
     // in several elements for a while.
     // See https://bugs.webkit.org/show_bug.cgi?id=77503 and related bugs.
     enum ShadowRootType {
         UserAgentShadowRoot = 0,
         AuthorShadowRoot
     };
 
-    static PassRefPtr<ShadowRoot> create(Document& document, ShadowRootType type)
+    static PassRefPtrWillBeRawPtr<ShadowRoot> create(Document& document, ShadowRootType type)
     {
-        return adoptRef(new ShadowRoot(document, type));
+        return adoptRefWillBeRefCountedGarbageCollected(new ShadowRoot(document, type));
     }
 
     void recalcStyle(StyleRecalcChange);
 
     // Disambiguate between Node and TreeScope hierarchies; TreeScope's implementation is simpler.
     using TreeScope::document;
     using TreeScope::getElementById;
 
     Element* host() const { return toElement(parentOrShadowHostNode()); }
     ElementShadow* owner() const { return host() ? host()->shadow() : 0; }
@@ skipping 88 matching lines @@
 {
     return adjustedFocusedElement();
 }
 
 DEFINE_NODE_TYPE_CASTS(ShadowRoot, isShadowRoot());
 DEFINE_TYPE_CASTS(ShadowRoot, TreeScope, treeScope, treeScope->rootNode().isShadowRoot(), treeScope.rootNode().isShadowRoot());
 
 } // namespace
 
 #endif