Remove tons of OILPAN.

sky/engine/core/editing/VisibleSelection.h

Index: sky/engine/core/editing/VisibleSelection.h
diff --git a/sky/engine/core/editing/VisibleSelection.h b/sky/engine/core/editing/VisibleSelection.h
index 3c2666da4349dca06e143ada930d7f19f8f998a2..6b5215e398bcfe442dbb4a5685347ad6bb507a85 100644
--- a/sky/engine/core/editing/VisibleSelection.h
+++ b/sky/engine/core/editing/VisibleSelection.h
@@ -123,15 +123,12 @@ public:
         ChangeObserver();
         virtual ~ChangeObserver();
         virtual void didChangeVisibleSelection() = 0;
-        virtual void trace(Visitor*) { }
     };
 
     void setChangeObserver(ChangeObserver&);
     void clearChangeObserver();
     void didChange(); // Fire the change observer, if any.
 
-    void trace(Visitor*);
-
     void validatePositionsIfNeeded();
 
 #ifndef NDEBUG