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

Source/core/svg/SVGTests.cpp

Index: Source/core/svg/SVGTests.cpp
diff --git a/Source/core/svg/SVGTests.cpp b/Source/core/svg/SVGTests.cpp
index 75281f1b92b135894d5800bbd5b109094ac491be..449a2507a0495a513c9b266d08807ede5157c42a 100644
--- a/Source/core/svg/SVGTests.cpp
+++ b/Source/core/svg/SVGTests.cpp
@@ -30,13 +30,21 @@
 
 namespace blink {
 
-SVGTests::SVGTests(SVGElement* contextElement)
-    : m_requiredFeatures(SVGStaticStringList::create(contextElement, SVGNames::requiredFeaturesAttr))
-    , m_requiredExtensions(SVGStaticStringList::create(contextElement, SVGNames::requiredExtensionsAttr))
-    , m_systemLanguage(SVGStaticStringList::create(contextElement, SVGNames::systemLanguageAttr))
+SVGTests::SVGTests()
 {
+}
+
+void SVGTests::initialize(SVGElement* contextElement)
+{
+    ASSERT(!m_requiredFeatures);
+    ASSERT(!m_requiredExtensions);
+    ASSERT(!m_systemLanguage);
     ASSERT(contextElement);
 
+    m_requiredFeatures = SVGStaticStringList::create(contextElement, SVGNames::requiredFeaturesAttr);
+    m_requiredExtensions = SVGStaticStringList::create(contextElement, SVGNames::requiredExtensionsAttr);
+    m_systemLanguage = SVGStaticStringList::create(contextElement, SVGNames::systemLanguageAttr);
+
     contextElement->addToPropertyMap(m_requiredFeatures);
     contextElement->addToPropertyMap(m_requiredExtensions);
     contextElement->addToPropertyMap(m_systemLanguage);