Prevents exiting presentation if triggering DON while presenting.

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 31fbc5f152979223fcafbeaa97bdcbe2648c76b2..3526d8b90a7ce122b67722993acf5b1ceb99cdc0 100644
--- a/third_party/WebKit/Source/modules/vr/VRDisplay.cpp
+++ b/third_party/WebKit/Source/modules/vr/VRDisplay.cpp
@@ -183,6 +183,11 @@ void ReportPresentationResult(PresentationResult result) {
 ScriptPromise VRDisplay::requestPresent(ScriptState* script_state,
                                         const HeapVector<VRLayer>& layers) {
   DVLOG(1) << __FUNCTION__;
+
+  if (in_display_activate_) {
+    requested_present_in_display_activate_ = true;
+  }
+
   ExecutionContext* execution_context = ExecutionContext::From(script_state);
   UseCounter::Count(execution_context, UseCounter::kVRRequestPresent);
   if (!execution_context->IsSecureContext()) {
@@ -300,7 +305,6 @@ ScriptPromise VRDisplay::requestPresent(ScriptState* script_state,
         submit_frame_client_binding_.CreateInterfacePtrAndBind(),
         ConvertToBaseCallback(
             WTF::Bind(&VRDisplay::OnPresentComplete, WrapPersistent(this))));
-    pending_present_request_ = true;

[mthiesse, 2017/05/10 20:12:38]

You should still set the flag here, or you'll do the wrong thing if presentation
fails above.

[tiborg, 2017/05/10 20:48:57]

I'm just reporting if the page requested present in the vrdisplayactivate
handler. If the presentation fails we should be in non-presenting mode anyways.
So, we don't have to stop presenting after the vrdisplayactivate handler is
done. Or am I missing something here?

   } else {
     UpdateLayerBounds();
     resolver->Resolve();
@@ -311,7 +315,6 @@ ScriptPromise VRDisplay::requestPresent(ScriptState* script_state,
 }
 
 void VRDisplay::OnPresentComplete(bool success) {
-  pending_present_request_ = false;
   if (success) {
     this->BeginPresent();
   } else {
@@ -685,7 +688,8 @@ void VRDisplay::OnActivate(device::mojom::blink::VRDisplayEventReason reason,
   AutoReset<bool> activating(&in_display_activate_, true);
   navigator_vr_->DispatchVREvent(VRDisplayEvent::Create(
       EventTypeNames::vrdisplayactivate, true, false, this, reason));
-  on_handled.Run(pending_present_request_);

[mthiesse, 2017/05/10 21:16:06]

I think we can simply change this to:
on_handled.Run(pending_present_request_ || is_presenting_);

And revert the rest of the changes.

[tiborg, 2017/05/16 15:27:01]

Done. And flipped switch as discussed offline.

+  on_handled.Run(requested_present_in_display_activate_);
+  requested_present_in_display_activate_ = false;
 }
 
 void VRDisplay::OnDeactivate(