Add support of vrdisplayconnect and vrdisplaydisconnect event

device/vr/vr_service.mojom

 // 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.
 
 module device;
 
 // A field of view, given by 4 degrees describing the view from a center point.
 struct VRFieldOfView {
   float upDegrees;
   float downDegrees;
@@ skipping 47 matching lines @@
   SetClient(VRServiceClient client);
 
   GetDisplays() => (array<VRDisplay> displays);
   [Sync]
   GetPose(uint32 index) => (VRPose pose);
   ResetPose(uint32 index);
 };
 
 interface VRServiceClient {
   OnDisplayChanged(VRDisplay display);
+  OnDisplayConnected(VRDisplay display);
+  OnDisplayDisconnected(uint32 index);
 };