Adding matrixTrasnform to DOMPointReadOnly interfaces as following spec.

third_party/WebKit/Source/core/dom/DOMPointReadOnly.cpp

 // 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.
 
 #include "core/dom/DOMPointReadOnly.h"
 
+#include "bindings/core/v8/ExceptionState.h"
 #include "bindings/core/v8/ScriptValue.h"
 #include "bindings/core/v8/V8ObjectBuilder.h"
+#include "core/dom/DOMMatrixInit.h"
+#include "core/dom/DOMMatrixReadOnly.h"
+#include "core/dom/DOMPoint.h"
 #include "core/dom/DOMPointInit.h"
 
 namespace blink {
 
 DOMPointReadOnly* DOMPointReadOnly::create(double x,
                                            double y,
                                            double z,
                                            double w) {
   return new DOMPointReadOnly(x, y, z, w);
 }
 
 ScriptValue DOMPointReadOnly::toJSONForBinding(
     ScriptState* scriptState) const {
   V8ObjectBuilder result(scriptState);
   result.addNumber("x", x());
   result.addNumber("y", y());
   result.addNumber("z", z());
   result.addNumber("w", w());
   return result.scriptValue();
 }
 
 DOMPointReadOnly* DOMPointReadOnly::fromPoint(const DOMPointInit& other) {
   return new DOMPointReadOnly(other.x(), other.y(), other.z(), other.w());
 }
 
+DOMPoint* DOMPointReadOnly::matrixTransform(DOMMatrixInit& other, ExceptionState& exceptionState) {

[zino, 2017/01/03 16:16:55]

nit: This line(and other lines) probably should be < 80 bytes.
As I know, the Blink coding style has been changed to Chromium style since last
Oct.

You can easily do it if using this command:
 git cl format third_party/WebKit/Source/core/dom/DOMPointReadOnly.cpp

[Byoungkwon Ko, 2017/01/03 16:35:39]

Done.

+  DOMMatrixReadOnly* matrix = DOMMatrixReadOnly::fromMatrix(other, exceptionState);
+
+  if (matrix->is2D() && z() == 0 && w() == 1) {
+    double transformedX = x() * matrix->m11() + y() * matrix->m12() + matrix->m41();
+    double transformedY = x() * matrix->m12() + y() * matrix->m22() + matrix->m42();
+    return DOMPoint::create(transformedX, transformedY, 0, 1);
+  }
+
+  double transformedX = x() * matrix->m11() + y() * matrix->m21() + z() * matrix->m31() +
+             w() * matrix->m41();
+  double transformedY = x() * matrix->m12() + y() * matrix->m22() + z() * matrix->m32() +
+             w() * matrix->m42();
+  double transformedZ = x() * matrix->m13() + y() * matrix->m23() + z() * matrix->m33() +
+             w() * matrix->m43();
+  double transformedW = x() * matrix->m14() + y() * matrix->m24() + z() * matrix->m34() +
+             w() * matrix->m44();
+  return DOMPoint::create(transformedX, transformedY, transformedZ, transformedW);
+}
+
 DOMPointReadOnly::DOMPointReadOnly(double x, double y, double z, double w)
     : m_x(x), m_y(y), m_z(z), m_w(w) {}
 
 }  // namespace blink