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

Source/core/html/canvas/Path2D.h

 /*
  * Copyright (C) 2012, 2013 Adobe Systems Incorporated. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 44 matching lines @@
         addPath(path, 0);
     }
 
     void addPath(Path2D* path, SVGMatrixTearOff* transform)
     {
         Path src = path->path();
         m_path.addPath(src, transform ? transform->value() : AffineTransform(1, 0, 0, 1, 0, 0));
     }
 
     virtual ~Path2D() { }
-    void trace(Visitor*) { }
+    virtual void trace(Visitor*) { }
 
 private:
     Path2D() : CanvasPathMethods()
     {
         ScriptWrappable::init(this);
     }
 
     Path2D(const Path& path)
         : CanvasPathMethods(path)
     {
         ScriptWrappable::init(this);
     }
 
     Path2D(Path2D* path)
         : CanvasPathMethods(path->path())
     {
         ScriptWrappable::init(this);
     }
 
     Path2D(const String& pathData)
         : CanvasPathMethods()
     {
         ScriptWrappable::init(this);
         buildPathFromString(pathData, m_path);
     }
 };
 
 }
 #endif