Implement vrdisplayactivate for GVR DON.

device/vr/android/gvr/gvr_device_provider.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_ANDROID_GVR_DEVICE_PROVIDER_H
 #define DEVICE_VR_ANDROID_GVR_DEVICE_PROVIDER_H
 
 #include <memory>
 
 #include "base/macros.h"
@@ skipping 21 matching lines @@
   void SetListeningForActivate(bool listening) override;
 
   // Called from GvrDevice.
   void RequestPresent(const base::Callback<void(bool)>& callback);
   void ExitPresent();
 
   void OnGvrDelegateReady(const base::WeakPtr<GvrDelegate>& delegate);
   void OnGvrDelegateRemoved();
   void OnDisplayBlur();
   void OnDisplayFocus();
+  void OnDisplayActivate();
 
  private:
   void SwitchToNonPresentingDelegate();
 
   std::unique_ptr<GvrDevice> vr_device_;
 
   base::WeakPtrFactory<GvrDeviceProvider> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(GvrDeviceProvider);
 };
 
 }  // namespace device
 
 #endif  // DEVICE_VR_ANDROID_GVR_DEVICE_PROVIDER_H