Initialize GC mixin bases only when leftmost vtable has been initialized.

Source/core/svg/SVGViewSpec.cpp

Index: Source/core/svg/SVGViewSpec.cpp
diff --git a/Source/core/svg/SVGViewSpec.cpp b/Source/core/svg/SVGViewSpec.cpp
index 57a9ac25be1d944bed8d2f280e3c1be424d2d376..9cf45c9678d0934ab5806f465bd310577422353d 100644
--- a/Source/core/svg/SVGViewSpec.cpp
+++ b/Source/core/svg/SVGViewSpec.cpp
@@ -35,10 +35,11 @@ SVGViewSpec::SVGViewSpec(SVGSVGElement* contextElement)
     // This contextElement will be only used for keeping this alive from the tearoff.
     // SVGSVGElement holds a strong-ref to this SVGViewSpec, so this is kept alive as:
     // AnimatedProperty tearoff -(contextElement)-> SVGSVGElement -(RefPtr)-> SVGViewSpec.
-    : SVGFitToViewBox(contextElement, PropertyMapPolicySkip)
-    , m_contextElement(contextElement)
+    : m_contextElement(contextElement)
     , m_transform(SVGAnimatedTransformList::create(contextElement, SVGNames::transformAttr, SVGTransformList::create()))
 {
+    SVGFitToViewBox::initialize(contextElement, PropertyMapPolicySkip);
+
     ASSERT(m_contextElement);
 
     viewBox()->setReadOnly();