Oilpan: revert SVG GC mixin constructor workaround.

Source/core/svg/SVGURIReference.h

 /*
  * Copyright (C) 2004, 2005, 2008, 2009 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005 Rob Buis <buis@kde.org>
  *
  * 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 40 matching lines @@
     }
 
     const String& hrefString() const { return m_href->currentValue()->value(); }
 
     // JS API
     SVGAnimatedString* href() const { return m_href.get(); }
 
     DECLARE_VIRTUAL_TRACE();
 
 protected:
-    SVGURIReference();
-
-    // FIXME: Oilpan: the construction of this mixin requires heap allocation,
-    // which cannot be safely done with Oilpan until the object that include
-    // this mixin have had its vptr initialized -- so as to be able to
-    // accurately trace the entire object should a GC strike while constructing
-    // the mixin.
-    //
-    // Try to come up with a more natural alternative and solution that doesn't
-    // require hoisting the constructor code for mixins into a separate method
-    // like initialize(). It makes construction of these heap-allocation mixins
-    // safe in the meantime, however.
-    //
-    void initialize(SVGElement*);
+    explicit SVGURIReference(SVGElement*);
 
 private:
     RefPtrWillBeMember<SVGAnimatedString> m_href;
 };
 
 } // namespace blink
 
 #endif // SVGURIReference_h