Consistently use on-heap collections for StyleRuleBase descendants.

Source/core/dom/TreeScopeStyleSheetCollection.h

Index: Source/core/dom/TreeScopeStyleSheetCollection.h
diff --git a/Source/core/dom/TreeScopeStyleSheetCollection.h b/Source/core/dom/TreeScopeStyleSheetCollection.h
index 6d24219c119b43ee0323e5406bd641f172dd51b8..d528f2be22bc1eafbe9fa05f60153d750606aeee 100644
--- a/Source/core/dom/TreeScopeStyleSheetCollection.h
+++ b/Source/core/dom/TreeScopeStyleSheetCollection.h
@@ -76,10 +76,12 @@ protected:
         Additive
     };
 
-    struct StyleSheetChange {
+    class StyleSheetChange {
+        STACK_ALLOCATED();
+    public:
         StyleResolverUpdateType styleResolverUpdateType;
         bool requiresFullStyleRecalc;
-        Vector<const StyleRuleFontFace*> fontFaceRulesToRemove;
+        WillBeHeapVector<RawPtrWillBeMember<const StyleRuleFontFace> > fontFaceRulesToRemove;
 
         StyleSheetChange()
             : styleResolverUpdateType(Reconstruct)
@@ -91,7 +93,7 @@ protected:
     void updateUsesRemUnits();
 
 private:
-    static StyleResolverUpdateType compareStyleSheets(const Vector<RefPtr<CSSStyleSheet> >& oldStyleSheets, const Vector<RefPtr<CSSStyleSheet> >& newStylesheets, Vector<StyleSheetContents*>& addedSheets);
+    static StyleResolverUpdateType compareStyleSheets(const Vector<RefPtr<CSSStyleSheet> >& oldStyleSheets, const Vector<RefPtr<CSSStyleSheet> >& newStylesheets, WillBeHeapVector<RawPtrWillBeMember<StyleSheetContents> >& addedSheets);
     bool activeLoadingStyleSheetLoaded(const Vector<RefPtr<CSSStyleSheet> >& newStyleSheets);
 
 protected: