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

device/vr/vr_device.cc

 // 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.
 
 #include "device/vr/vr_device.h"
 #include "device/vr/vr_device_provider.h"
 #include "device/vr/vr_display_impl.h"
 
 namespace device {
 
@@ skipping 51 matching lines @@
 void VRDevice::OnBlur() {
   for (auto* display : displays_)
     display->OnBlur();
 }
 
 void VRDevice::OnFocus() {
   for (auto* display : displays_)
     display->OnFocus();
 }
 
-void VRDevice::OnActivate(mojom::VRDisplayEventReason reason) {
+void VRDevice::OnActivate(mojom::VRDisplayEventReason reason,
+                          const base::Callback<void(bool)>& on_handled) {
   for (auto* display : displays_)
-    display->OnActivate(reason);
+    display->OnActivate(reason, on_handled);
 }
 
 void VRDevice::OnDeactivate(mojom::VRDisplayEventReason reason) {
   for (auto* display : displays_)
     display->OnDeactivate(reason);
 }
 
 void VRDevice::SetPresentingDisplay(VRDisplayImpl* display) {
   presenting_display_ = display;
 }
 
 }  // namespace device