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

Source/core/css/resolver/StyleResolver.h

Index: Source/core/css/resolver/StyleResolver.h
diff --git a/Source/core/css/resolver/StyleResolver.h b/Source/core/css/resolver/StyleResolver.h
index a848bb439c6f687ca1316a12b5bb1e40fd20a054..bd00a24815e171924f2a1eb0f0edd4a547e3a8d5 100644
--- a/Source/core/css/resolver/StyleResolver.h
+++ b/Source/core/css/resolver/StyleResolver.h
@@ -306,6 +306,9 @@ private:
 
     RefPtr<ViewportStyleResolver> m_viewportStyleResolver;
 
+    // FIXME: Oilpan: This should be a WillBePersistentHeapListHashSet.
+    // This is safe for now, but should be updated when we support
+    // heap allocated ListHashSets.
     ListHashSet<CSSStyleSheet*, 16> m_pendingStyleSheets;
 
     ScopedStyleTree m_styleTree;