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

device/vr/vr_device.h

 // 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.
 
 #ifndef DEVICE_VR_VR_DEVICE_H
 #define DEVICE_VR_VR_DEVICE_H
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "device/vr/vr_export.h"
@@ skipping 36 matching lines @@
   virtual void AddDisplay(VRDisplayImpl* display);
   virtual void RemoveDisplay(VRDisplayImpl* display);
 
   virtual bool IsAccessAllowed(VRDisplayImpl* display);
   virtual bool CheckPresentingDisplay(VRDisplayImpl* display);
 
   virtual void OnChanged();
   virtual void OnExitPresent();
   virtual void OnBlur();
   virtual void OnFocus();
-  virtual void OnActivate(mojom::VRDisplayEventReason reason);
+  virtual void OnActivate(mojom::VRDisplayEventReason reason,
+                          const base::Callback<void(bool)>& on_handled);
   virtual void OnDeactivate(mojom::VRDisplayEventReason reason);
 
  protected:
   friend class VRDisplayImpl;
   friend class VRDisplayImplTest;
 
   void SetPresentingDisplay(VRDisplayImpl* display);
 
  private:
   void OnVRDisplayInfoCreated(mojom::VRDisplayInfoPtr vr_device_info);
 
   std::set<VRDisplayImpl*> displays_;
 
   VRDisplayImpl* presenting_display_;
 
   unsigned int id_;
 
   static unsigned int next_id_;
 
   base::WeakPtrFactory<VRDevice> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(VRDevice);
 };
 
 }  // namespace device
 
 #endif  // DEVICE_VR_VR_DEVICE_H