Remove tons of OILPAN.

sky/engine/core/dom/DocumentStyleSheetCollection.h

Index: sky/engine/core/dom/DocumentStyleSheetCollection.h
diff --git a/sky/engine/core/dom/DocumentStyleSheetCollection.h b/sky/engine/core/dom/DocumentStyleSheetCollection.h
index dc60006240028ab40eb47b360603db7dc94b4bb6..5fe109e7f9a4a0a82e7aa90020d51345b0a69c87 100644
--- a/sky/engine/core/dom/DocumentStyleSheetCollection.h
+++ b/sky/engine/core/dom/DocumentStyleSheetCollection.h
@@ -48,11 +48,6 @@ public:
     void updateActiveStyleSheets(StyleEngine*, StyleResolverUpdateMode);
     void collectStyleSheets(StyleEngine*, DocumentStyleSheetCollector&);
 
-    virtual void trace(Visitor* visitor) override
-    {
-        TreeScopeStyleSheetCollection::trace(visitor);
-    }
-
 private:
     explicit DocumentStyleSheetCollection(TreeScope&);