Implement *multiply*() methods in DOMMatrix.

Source/core/dom/DOMMatrix.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 DOMMatrix_h
 #define DOMMatrix_h
 
 #include "core/dom/DOMMatrixReadOnly.h"
 
 namespace blink {
@@ skipping 20 matching lines @@
     void setM24(double value) { m_matrix.setM24(value); setIs2D(!value); }
     void setM31(double value) { m_matrix.setM31(value); setIs2D(!value); }
     void setM32(double value) { m_matrix.setM32(value); setIs2D(!value); }
     void setM33(double value) { m_matrix.setM33(value); setIs2D(value != 1); }
     void setM34(double value) { m_matrix.setM34(value); setIs2D(!value); }
     void setM41(double value) { m_matrix.setM41(value); }
     void setM42(double value) { m_matrix.setM42(value); }
     void setM43(double value) { m_matrix.setM43(value); setIs2D(!value); }
     void setM44(double value) { m_matrix.setM44(value); setIs2D(value != 1); }
 
+    DOMMatrix* multiplySelf(DOMMatrix*);
+    DOMMatrix* preMultiplySelf(DOMMatrix*);
     DOMMatrix* translateSelf(double tx, double ty, double tz = 0);
     DOMMatrix* scaleSelf(double scale, double ox = 0, double oy = 0);
     DOMMatrix* scale3dSelf(double scale, double ox = 0, double oy = 0, double oz = 0);
     DOMMatrix* scaleNonUniformSelf(double sx, double sy = 1, double sz = 1,
         double ox = 0, double oy = 0, double oz = 0);
 
 private:
     DOMMatrix(const TransformationMatrix&, bool is2D = true);
 
     void setIs2D(bool value);
 };
 
 } // namespace blink
 
 #endif