Oilpan: revert SVG GC mixin constructor workaround.

Source/core/svg/SVGFitToViewBox.h

Index: Source/core/svg/SVGFitToViewBox.h
diff --git a/Source/core/svg/SVGFitToViewBox.h b/Source/core/svg/SVGFitToViewBox.h
index 5e05c99137c04de158cf117c0dac9135707eb10c..db2bd05955391e8d3828acc5d00c17dbbde13299 100644
--- a/Source/core/svg/SVGFitToViewBox.h
+++ b/Source/core/svg/SVGFitToViewBox.h
@@ -73,21 +73,7 @@ public:
     DECLARE_VIRTUAL_TRACE();
 
 protected:
-    SVGFitToViewBox();
-
-    // 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* contextElement, PropertyMapPolicy = PropertyMapPolicyAdd);
-
+    explicit SVGFitToViewBox(SVGElement*, PropertyMapPolicy = PropertyMapPolicyAdd);
     void updateViewBox(const FloatRect&);
     void clearViewBox() { m_viewBox = nullptr; }
     void clearPreserveAspectRatio() { m_preserveAspectRatio = nullptr; }