Tentatively goes into WebVR presentation mode if page listens to vrdisplayactivate.

device/vr/test/fake_vr_display_impl_client.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_TEST_FAKE_VR_DISPLAY_IMPL_CLIENT_H_
 #define DEVICE_VR_TEST_FAKE_VR_DISPLAY_IMPL_CLIENT_H_
 
 #include "device/vr/vr_display_impl.h"
 #include "device/vr/vr_service.mojom.h"
 #include "mojo/public/cpp/bindings/binding.h"
 #include "mojo/public/cpp/bindings/interface_request.h"
 
 namespace device {
 class FakeVRServiceClient;
 
 class FakeVRDisplayImplClient : public mojom::VRDisplayClient {
  public:
   FakeVRDisplayImplClient(mojom::VRDisplayClientRequest request);
   ~FakeVRDisplayImplClient() override;
 
   void SetServiceClient(FakeVRServiceClient* service_client);
   void OnChanged(mojom::VRDisplayInfoPtr display) override;
   void OnExitPresent() override {}
   void OnBlur() override {}
   void OnFocus() override {}
-  void OnActivate(mojom::VRDisplayEventReason reason) override {}
+  void OnActivate(mojom::VRDisplayEventReason reason,
+                  const OnActivateCallback& callback) override {}
   void OnDeactivate(mojom::VRDisplayEventReason reason) override {}
 
  private:
   FakeVRServiceClient* service_client_;
   mojom::VRDisplayInfoPtr last_display_;
   mojo::Binding<mojom::VRDisplayClient> m_binding_;
 
   DISALLOW_COPY_AND_ASSIGN(FakeVRDisplayImplClient);
 };
 
 }  // namespace device
 
 #endif  // DEVICE_VR_TEST_FAKE_VR_DISPLAY_IMPL_CLIENT_H_