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

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

Index: third_party/WebKit/Source/modules/vr/VRDisplay.cpp
diff --git a/third_party/WebKit/Source/modules/vr/VRDisplay.cpp b/third_party/WebKit/Source/modules/vr/VRDisplay.cpp
index 553622a0dfa064f16522cfd8694dc7834f1abb48..1c8baa8e33f1f4f2879fee6898498cddea9fff7f 100644
--- a/third_party/WebKit/Source/modules/vr/VRDisplay.cpp
+++ b/third_party/WebKit/Source/modules/vr/VRDisplay.cpp
@@ -295,6 +295,7 @@ ScriptPromise VRDisplay::requestPresent(ScriptState* script_state,
         submit_frame_client_binding_.CreateInterfacePtrAndBind(),
         ConvertToBaseCallback(
             WTF::Bind(&VRDisplay::OnPresentComplete, WrapPersistent(this))));
+    pending_present_request_ = true;
   } else {
     UpdateLayerBounds();
     resolver->Resolve();
@@ -305,6 +306,7 @@ ScriptPromise VRDisplay::requestPresent(ScriptState* script_state,
 }
 
 void VRDisplay::OnPresentComplete(bool success) {
+  pending_present_request_ = false;
   if (success) {
     this->BeginPresent();
   } else {
@@ -661,10 +663,12 @@ void VRDisplay::StopPresenting() {
   pending_previous_frame_render_ = false;
 }
 
-void VRDisplay::OnActivate(device::mojom::blink::VRDisplayEventReason reason) {
+void VRDisplay::OnActivate(device::mojom::blink::VRDisplayEventReason reason,
+                           const OnActivateCallback& on_handled) {
   AutoReset<bool> activating(&in_display_activate_, true);
   navigator_vr_->DispatchVREvent(VRDisplayEvent::Create(
       EventTypeNames::vrdisplayactivate, true, false, this, reason));
+  on_handled.Run(pending_present_request_);
 }
 
 void VRDisplay::OnDeactivate(