Update WebVR API based on prerelease 1.1 except window and navigator interface

third_party/WebKit/Source/modules/vr/VRDisplayEvent.idl

 // 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.
 
 enum VRDisplayEventReason {
-    "connected",
-    "disconnected",
+    "mounted",
     "navigation",
-    "mounted",
     "unmounted"
 };
 
 // https://w3c.github.io/webvr/#interface-vrdisplayevent
 [
     OriginTrialEnabled=WebVR,
-    Constructor(DOMString type, optional VRDisplayEventInit eventInitDict),
+    Constructor(DOMString type, VRDisplayEventInit eventInitDict),
 ] interface VRDisplayEvent : Event {
     readonly attribute VRDisplay display;
-    readonly attribute VRDisplayEventReason reason;
+    readonly attribute VRDisplayEventReason? reason;
 };