Add support of vrdisplayconnect and vrdisplaydisconnect event

device/vr/vr_client_dispatcher.h

 // 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.
 
 #ifndef DEVICE_VR_VR_CLIENT_DISPATCHER_H
 #define DEVICE_VR_VR_CLIENT_DISPATCHER_H
 
 #include "device/vr/vr_service.mojom.h"
 
 namespace device {
 
+class VRDevice;
+
 class VRClientDispatcher {
  public:
   virtual void OnDeviceChanged(VRDisplayPtr device) = 0;
+  virtual void OnDeviceConnectionStatusChanged(VRDevice* device,
+                                               bool is_connected) = 0;
 };
 
 }  // namespace device
 
 #endif  // DEVICE_VR_VR_CLIENT_DISPATCHER_H