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

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 f2141c396fd3c73694e795115f2f0b27fa91bbcc..6d7b976c6897829e582f04eb5eb5c1351b83ab41 100644
--- a/Source/core/dom/TreeScopeStyleSheetCollection.h
+++ b/Source/core/dom/TreeScopeStyleSheetCollection.h
@@ -56,7 +56,6 @@ public:
     void removeStyleSheetCandidateNode(Node*, ContainerNode* scopingNode);
     bool hasStyleSheetCandidateNodes() const { return !m_styleSheetCandidateNodes.isEmpty(); }
 
-
     bool usesRemUnits() const { return m_usesRemUnits; }
 
     DocumentOrderedList& styleSheetCandidateNodes() { return m_styleSheetCandidateNodes; }
@@ -65,6 +64,11 @@ public:
 
     void clearMediaQueryRuleSetStyleSheets();
 
+    virtual void trace(Visitor* visitor) OVERRIDE
+    {
+        StyleSheetCollection::trace(visitor);
+    }
+
 protected:
     explicit TreeScopeStyleSheetCollection(TreeScope&);