Oilpan: Ensure that classes with virtual trace methods always have vtables for their left-most base…

Source/core/html/canvas/HitRegion.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef HitRegion_h
 #define HitRegion_h
 
 #include "bindings/core/v8/Dictionary.h"
 #include "core/dom/Element.h"
 #include "platform/graphics/Path.h"
@@ skipping 28 matching lines @@
     void removePixels(const Path&);
     void updateAccessibility(Element* canvas);
 
     bool contains(const LayoutPoint&) const;
 
     const String& id() const { return m_id; }
     const Path& path() const { return m_path; }
     Element* control() const { return m_control.get(); }
     WindRule fillRule() const { return m_fillRule; }
 
-    void trace(Visitor*);
+    virtual void trace(Visitor*);
 
 private:
     explicit HitRegion(const HitRegionOptions&);
 
     String m_id;
     RefPtrWillBeMember<Element> m_control;
     Path m_path;
     WindRule m_fillRule;
 };
 
@@ skipping 28 matching lines @@
     typedef WillBeHeapHashMap<RefPtrWillBeMember<Element>, RefPtrWillBeMember<HitRegion> > HitRegionControlMap;
 
     HitRegionList m_hitRegionList;
     HitRegionIdMap m_hitRegionIdMap;
     HitRegionControlMap m_hitRegionControlMap;
 };
 
 } // namespace blink
 
 #endif