Implement DOMQuad of geometry interfaces.

Source/core/dom/DOMQuad.idl

+// Copyright 2015 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.
+
+// http://dev.w3.org/fxtf/geometry/#DOMQuad
+
+[
+    // FIXME: The point argument is optional in the spec:
+    // https://www.w3.org/Bugs/Public/show_bug.cgi?id=28108
+    Constructor(DOMRectInit rect),
+    Constructor(optional DOMPointInit p1, optional DOMPointInit p2,
+                optional DOMPointInit p3, optional DOMPointInit p4),
+    // FIXME: Exposed=(Window,Worker)
+    GarbageCollected,
+    RuntimeEnabled=GeometryInterfaces,
+] interface DOMQuad {
+    readonly attribute DOMPoint p1;
+    readonly attribute DOMPoint p2;
+    readonly attribute DOMPoint p3;
+    readonly attribute DOMPoint p4;
+    readonly attribute DOMRectReadOnly bounds;
+};