Implement DOMQuad of geometry interfaces.

Source/core/dom/DOMPoint.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 DOMPoint_h
 #define DOMPoint_h
 
 #include "core/dom/DOMPointReadOnly.h"
 
 namespace blink {
 
 class DOMPointInit;
 
-class DOMPoint final : public DOMPointReadOnly {
+class DOMPoint : public DOMPointReadOnly {
     DEFINE_WRAPPERTYPEINFO();
 public:
     static DOMPoint* create(const DOMPointInit&);
-    static DOMPoint* create(double x, double y, double z = 0, double w = 1);
+    static DOMPoint* create(double x = 0, double y = 0, double z = 0, double w = 1);
 
-    void setX(double x) { m_x = x; }
-    void setY(double y) { m_y = y; }
+    virtual void setX(double x) { m_x = x; }
+    virtual void setY(double y) { m_y = y; }
     void setZ(double z) { m_z = z; }
     void setW(double w) { m_w = w; }
 
 protected:
     DOMPoint(double x, double y, double z, double w);
 };
 
 } // namespace blink
 
 #endif