Oilpan: cleanup based on review comments after removal of TreeShared.

Source/core/svg/SVGElement.h

Index: Source/core/svg/SVGElement.h
diff --git a/Source/core/svg/SVGElement.h b/Source/core/svg/SVGElement.h
index c20377b6a6329911214dd86fbe5c94fc69c760f0..adc6ba86c660ba343a62ea7bad0a86051a499963 100644
--- a/Source/core/svg/SVGElement.h
+++ b/Source/core/svg/SVGElement.h
@@ -107,7 +107,7 @@ public:
     void invalidateSVGAttributes() { ensureUniqueElementData().m_animatedSVGAttributesAreDirty = true; }
     void invalidateSVGPresentationAttributeStyle() { ensureUniqueElementData().m_presentationAttributeStyleIsDirty = true; }
 
-    const HashSet<SVGElement*>& instancesForElement() const;
+    const WillBeHeapHashSet<RawPtrWillBeWeakMember<SVGElement> >& instancesForElement() const;
     void mapInstanceToElement(SVGElement*);
     void removeInstanceMapping(SVGElement*);
 
@@ -115,6 +115,7 @@ public:
 
     void setCursorElement(SVGCursorElement*);
     void setCursorImageValue(CSSCursorImageValue*);
+
 #if !ENABLE(OILPAN)
     void cursorElementRemoved();
     void cursorImageValueRemoved();