Oilpan: move SVG property hierarchy to the heap.

Source/core/svg/SVGForeignObjectElement.h

Index: Source/core/svg/SVGForeignObjectElement.h
diff --git a/Source/core/svg/SVGForeignObjectElement.h b/Source/core/svg/SVGForeignObjectElement.h
index fb4fdfdfb76b2dbe6d657ea9bc5aa08a9a649809..cd89c9f14582e4233adb64e6ed2865249c7d0f4e 100644
--- a/Source/core/svg/SVGForeignObjectElement.h
+++ b/Source/core/svg/SVGForeignObjectElement.h
@@ -25,6 +25,7 @@
 #include "core/svg/SVGAnimatedLength.h"
 #include "core/svg/SVGGraphicsElement.h"
 #include "core/svg/SVGURIReference.h"
+#include "platform/heap/Handle.h"
 
 namespace blink {
 
@@ -38,6 +39,8 @@ public:
     SVGAnimatedLength* width() const { return m_width.get(); }
     SVGAnimatedLength* height() const { return m_height.get(); }
 
+    virtual void trace(Visitor*) override;
+
 private:
     explicit SVGForeignObjectElement(Document&);
 
@@ -52,10 +55,10 @@ private:
 
     virtual bool selfHasRelativeLengths() const override;
 
-    RefPtr<SVGAnimatedLength> m_x;
-    RefPtr<SVGAnimatedLength> m_y;
-    RefPtr<SVGAnimatedLength> m_width;
-    RefPtr<SVGAnimatedLength> m_height;
+    RefPtrWillBeMember<SVGAnimatedLength> m_x;
+    RefPtrWillBeMember<SVGAnimatedLength> m_y;
+    RefPtrWillBeMember<SVGAnimatedLength> m_width;
+    RefPtrWillBeMember<SVGAnimatedLength> m_height;
 };
 
 } // namespace blink