Oilpan: revert SVG GC mixin constructor workaround.

Source/core/svg/SVGURIReference.h

Index: Source/core/svg/SVGURIReference.h
diff --git a/Source/core/svg/SVGURIReference.h b/Source/core/svg/SVGURIReference.h
index 210f51768c7b4c1f88d27944cb34502e8c0bbe6c..af3f75913f8de9d900042d9d028d96da8fc9774b 100644
--- a/Source/core/svg/SVGURIReference.h
+++ b/Source/core/svg/SVGURIReference.h
@@ -58,20 +58,7 @@ public:
     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;