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

third_party/WebKit/Source/modules/vr/VRDisplay.h

Index: third_party/WebKit/Source/modules/vr/VRDisplay.h
diff --git a/third_party/WebKit/Source/modules/vr/VRDisplay.h b/third_party/WebKit/Source/modules/vr/VRDisplay.h
index 16dead3e91412fcc91c619032c2c18ad0ba7448c..8a3682a5edbb7d604bfd8787af038c742ac4c530 100644
--- a/third_party/WebKit/Source/modules/vr/VRDisplay.h
+++ b/third_party/WebKit/Source/modules/vr/VRDisplay.h
@@ -130,7 +130,8 @@ class VRDisplay final : public EventTargetWithInlineData,
   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,
@@ -188,6 +189,7 @@ class VRDisplay final : public EventTargetWithInlineData,
   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_;