Geometry: Reimplement DOMPoint using V8 extras.

third_party/WebKit/Source/modules/geometry/DOMPointReadOnly.js

+// Copyright 2016 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.
+
+(function(global, binding, v8) {
+  'use strict';
+
+  const defineProperty = global.Object.defineProperty;
+
+  const _x = binding.domPointX = v8.createPrivateSymbol('[[x]]');
+  const _y = binding.domPointY = v8.createPrivateSymbol('[[y]]');
+  const _z = binding.domPointZ = v8.createPrivateSymbol('[[z]]');
+  const _w = binding.domPointW = v8.createPrivateSymbol('[[w]]');
+
+  function ensureDOMPoint(obj) {
+    if (!(_x in obj))
+      throw new TypeError('Illegal invocation');
+  }
+
+  class DOMPointReadOnly {
+    constructor(x = 0, y = 0, z = 0, w = 1) {
+      this[_x] = +x;
+      this[_y] = +y;
+      this[_z] = +z;
+      this[_w] = +w;
+    }
+
+    get x() {
+      ensureDOMPoint(this);
+      return this[_x];
+    }
+
+    get y() {
+      ensureDOMPoint(this);
+      return this[_y];
+    }
+
+    get z() {
+      ensureDOMPoint(this);
+      return this[_z];
+    }
+
+    get w() {
+      ensureDOMPoint(this);
+      return this[_w];
+    }
+
+    static fromPoint(init) {
+      return new DOMPointReadOnly(init.x, init.y, init.z, init.w);
+    }
+  }
+
+  binding.createDOMPointReadOnly = (x, y, z, w) =>
+      new DOMPointReadOnly(x, y, z, w);
+  binding.ensureDOMPoint = ensureDOMPoint;
+
+  defineProperty(global, 'DOMPointReadOnly', {
+    value: DOMPointReadOnly,
+    configurable: true,
+    enumerable: false,
+    writable: true
+  });
+});