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 5d6c5068a9c87332d7038c7e077c160aa70a8bee..2ced71a04d16043e65c8515edee005785dbb06b6 100644
--- a/Source/core/css/CSSStyleSheet.h
+++ b/Source/core/css/CSSStyleSheet.h
@@ -93,13 +93,14 @@ 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();