Adding matrixTrasnform to DOMPointReadOnly interfaces as following spec.

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

Index: third_party/WebKit/Source/core/dom/DOMPointReadOnly.cpp
diff --git a/third_party/WebKit/Source/core/dom/DOMPointReadOnly.cpp b/third_party/WebKit/Source/core/dom/DOMPointReadOnly.cpp
index 6857417126483ece74e48bc256f035885c371f75..d8c93677b60a5f59a469345851e99452d5c45547 100644
--- a/third_party/WebKit/Source/core/dom/DOMPointReadOnly.cpp
+++ b/third_party/WebKit/Source/core/dom/DOMPointReadOnly.cpp
@@ -4,8 +4,12 @@
 
 #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 {
@@ -31,6 +35,27 @@ DOMPointReadOnly* DOMPointReadOnly::fromPoint(const DOMPointInit& other) {
   return new DOMPointReadOnly(other.x(), other.y(), other.z(), other.w());
 }
 
+DOMPoint* DOMPointReadOnly::matrixTransform(DOMMatrixInit& other, ExceptionState& exceptionState) {
+  DOMPoint* point = DOMPoint::create(x(), y(), z(), w());

[zino, 2016/12/28 16:39:14]

This is unnecessary. You don't need to create this object twice.
Instead you can use just x(), y(), z(), w() and then return final result.

(Actually, we can use DOMMatrixReadOnly::transformPoint but it's not a good way
for performance.)

[Byoungkwon Ko, 2017/01/03 15:54:37]

Done.

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