Implement *multiply*() methods in DOMMatrix.

Source/core/dom/DOMMatrixReadOnly.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 DOMMatrixReadOnly_h
 #define DOMMatrixReadOnly_h
 
 #include "bindings/core/v8/ScriptWrappable.h"
 #include "platform/heap/Handle.h"
 #include "platform/transforms/TransformationMatrix.h"
@@ skipping 26 matching lines @@
     double m33() const { return m_matrix.m33(); }
     double m34() const { return m_matrix.m34(); }
     double m41() const { return m_matrix.m41(); }
     double m42() const { return m_matrix.m42(); }
     double m43() const { return m_matrix.m43(); }
     double m44() const { return m_matrix.m44(); }
 
     bool is2D() const;
     bool isIdentity() const;
 
+    DOMMatrix* multiply(DOMMatrix*);
     DOMMatrix* translate(double tx, double ty, double tz = 0);
     DOMMatrix* scale(double scale, double ox = 0, double oy = 0);
     DOMMatrix* scale3d(double scale, double ox = 0, double oy = 0, double oz = 0);
     DOMMatrix* scaleNonUniform(double sx, double sy = 1, double sz = 1,
         double ox = 0, double oy = 0, double oz = 0);
 
     PassRefPtr<Float32Array> toFloat32Array() const;
     PassRefPtr<Float64Array> toFloat64Array() const;
 
     const TransformationMatrix& matrix() const { return m_matrix; }
 
     void trace(Visitor*) { }
 
 protected:
     TransformationMatrix m_matrix;
     bool m_is2D;
 };
 
 } // namespace blink
 
 #endif