Oilpan: move SVG property hierarchy to the heap.

Source/core/svg/SVGLinearGradientElement.h

Index: Source/core/svg/SVGLinearGradientElement.h
diff --git a/Source/core/svg/SVGLinearGradientElement.h b/Source/core/svg/SVGLinearGradientElement.h
index aaca251aba3177ac62de64b69f4ade4bfef8e81f..bc7ce28fccf23b197e92b3c902f79752a25192f8 100644
--- a/Source/core/svg/SVGLinearGradientElement.h
+++ b/Source/core/svg/SVGLinearGradientElement.h
@@ -24,6 +24,7 @@
 #include "core/SVGNames.h"
 #include "core/svg/SVGAnimatedLength.h"
 #include "core/svg/SVGGradientElement.h"
+#include "platform/heap/Handle.h"
 
 namespace blink {
 
@@ -41,6 +42,8 @@ public:
     SVGAnimatedLength* x2() const { return m_x2.get(); }
     SVGAnimatedLength* y2() const { return m_y2.get(); }
 
+    virtual void trace(Visitor*) override;
+
 private:
     explicit SVGLinearGradientElement(Document&);
 
@@ -52,10 +55,10 @@ private:
 
     virtual bool selfHasRelativeLengths() const override;
 
-    RefPtr<SVGAnimatedLength> m_x1;
-    RefPtr<SVGAnimatedLength> m_y1;
-    RefPtr<SVGAnimatedLength> m_x2;
-    RefPtr<SVGAnimatedLength> m_y2;
+    RefPtrWillBeMember<SVGAnimatedLength> m_x1;
+    RefPtrWillBeMember<SVGAnimatedLength> m_y1;
+    RefPtrWillBeMember<SVGAnimatedLength> m_x2;
+    RefPtrWillBeMember<SVGAnimatedLength> m_y2;
 };
 
 } // namespace blink