Oilpan: make DocumentFragment a heap allocated object.

Source/core/dom/shadow/ShadowRoot.h

Index: Source/core/dom/shadow/ShadowRoot.h
diff --git a/Source/core/dom/shadow/ShadowRoot.h b/Source/core/dom/shadow/ShadowRoot.h
index 4c0fabd1b59d7f2b6f55a88e3b9557c93630229c..64b243973464cdc83e1ee4b92230ee208904ff78 100644
--- a/Source/core/dom/shadow/ShadowRoot.h
+++ b/Source/core/dom/shadow/ShadowRoot.h
@@ -55,9 +55,9 @@ public:
         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);