Oilpan: Reapply: Remove all the RefPtrs and most of the raw pointers to style

Source/core/css/CSSStyleSheet.h

Index: Source/core/css/CSSStyleSheet.h
diff --git a/Source/core/css/CSSStyleSheet.h b/Source/core/css/CSSStyleSheet.h
index ab7106e6bb86cd24a2665396370c8cb913c4baff..2dd5f654dc0511a6f877d517513c0a1563639eb2 100644
--- a/Source/core/css/CSSStyleSheet.h
+++ b/Source/core/css/CSSStyleSheet.h
@@ -92,13 +92,14 @@ public:
 
     class RuleMutationScope {
         WTF_MAKE_NONCOPYABLE(RuleMutationScope);
+        STACK_ALLOCATED();
     public:
-        RuleMutationScope(CSSStyleSheet*);
-        RuleMutationScope(CSSRule*);
+        explicit RuleMutationScope(CSSStyleSheet*);
+        explicit RuleMutationScope(CSSRule*);
         ~RuleMutationScope();
 
     private:
-        CSSStyleSheet* m_styleSheet;
+        RawPtrWillBeMember<CSSStyleSheet> m_styleSheet;
     };
 
     void willMutateRules();