Revert of [oilpan]: Remove support for tracing off-heap hashmaps.

Source/core/html/forms/FormController.cpp

 /*
  * Copyright (C) 2006, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2010, 2011, 2012 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 276 matching lines @@
 }
 
 // ----------------------------------------------------------------------------
 
 class FormKeyGenerator FINAL : public NoBaseWillBeGarbageCollectedFinalized<FormKeyGenerator> {
     WTF_MAKE_NONCOPYABLE(FormKeyGenerator);
     WTF_MAKE_FAST_ALLOCATED_WILL_BE_REMOVED;
 
 public:
     static PassOwnPtrWillBeRawPtr<FormKeyGenerator> create() { return adoptPtrWillBeNoop(new FormKeyGenerator); }
-    void trace(Visitor* visitor)
-    {
-#if ENABLE(OILPAN)
-        visitor->trace(m_formToKeyMap);
-#endif
-    }
+    void trace(Visitor* visitor) { visitor->trace(m_formToKeyMap); }
     const AtomicString& formKey(const HTMLFormControlElementWithState&);
     void willDeleteForm(HTMLFormElement*);
 
 private:
     FormKeyGenerator() { }
 
     typedef WillBeHeapHashMap<RawPtrWillBeMember<HTMLFormElement>, AtomicString> FormToKeyMap;
     typedef HashMap<String, unsigned> FormSignatureToNextIndexMap;
     FormToKeyMap m_formToKeyMap;
     FormSignatureToNextIndexMap m_formSignatureToNextIndexMap;
@@ skipping 247 matching lines @@
 {
     m_documentState->addControl(&control);
 }
 
 void FormController::unregisterStatefulFormControl(HTMLFormControlElementWithState& control)
 {
     m_documentState->removeControl(&control);
 }
 
 } // namespace blink