[WIP] Implement DOMPoint of geometry interface.

Source/core/dom/DOMPointReadOnly.idl

+// 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.
+
+[
+    GarbageCollected,
+    RuntimeEnabled=GeometryInterface,
+] interface DOMPointReadOnly {
+    [ImplementedInPrivateScript] readonly attribute unrestricted double x;
+    [ImplementedInPrivateScript] readonly attribute unrestricted double y;
+    [ImplementedInPrivateScript] readonly attribute unrestricted double z;
+    [ImplementedInPrivateScript] readonly attribute unrestricted double w;
+
+    // FIXME: We should implement DOMMatrixReadOnly interface.
+    // [ImplementedInPrivateScript] DOMPoint matrixTransform(DOMMatrixReadOnly matrix);
+};