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

third_party/WebKit/Source/modules/vr/VRDisplay.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 VRDisplay_h
 #define VRDisplay_h
 
 #include "core/dom/Document.h"
 #include "core/dom/FrameRequestCallback.h"
 #include "core/events/EventTarget.h"
@@ skipping 112 matching lines @@
 
   // VRSubmitFrameClient
   void OnSubmitFrameTransferred();
   void OnSubmitFrameRendered();
 
   // VRDisplayClient
   void OnChanged(device::mojom::blink::VRDisplayInfoPtr) override;
   void OnExitPresent() override;
   void OnBlur() override;
   void OnFocus() override;
-  void OnActivate(device::mojom::blink::VRDisplayEventReason) override;
+  void OnActivate(device::mojom::blink::VRDisplayEventReason,
+                  const OnActivateCallback& on_handled) override;
   void OnDeactivate(device::mojom::blink::VRDisplayEventReason) override;
 
   void OnVSync(device::mojom::blink::VRPosePtr,
                mojo::common::mojom::blink::TimeDeltaPtr,
                int16_t frame_id,
                device::mojom::blink::VRVSyncProvider::Status);
   void ConnectVSyncProvider();
   void OnVSyncConnectionError();
 
   ScriptedAnimationController& EnsureScriptedAnimationController(Document*);
@@ skipping 37 matching lines @@
   Member<ScriptedAnimationController> scripted_animation_controller_;
   bool pending_raf_ = false;
   bool pending_vsync_ = false;
   bool in_animation_frame_ = false;
   bool in_display_activate_ = false;
   bool display_blurred_ = false;
   double timebase_ = -1;
   bool pending_previous_frame_render_ = false;
   bool pending_submit_frame_ = false;
   bool v_sync_connection_failed_ = false;
+  bool pending_present_request_ = false;
 
   device::mojom::blink::VRDisplayPtr display_;
 
   mojo::Binding<device::mojom::blink::VRSubmitFrameClient>
       submit_frame_client_binding_;
   mojo::Binding<device::mojom::blink::VRDisplayClient> display_client_binding_;
   device::mojom::blink::VRVSyncProviderPtr vr_v_sync_provider_;
 
   HeapDeque<Member<ScriptPromiseResolver>> pending_present_resolvers_;
 };
@@ skipping 16 matching lines @@
   kRequestDenied = 12,
   kFullscreenNotEnabled = 13,
   kPresentationResultMax,  // Must be last member of enum.
 };
 
 void ReportPresentationResult(PresentationResult);
 
 }  // namespace blink
 
 #endif  // VRDisplay_h