Prevents exiting presentation if triggering DON while presenting.

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

 // 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.
 
 #include "modules/vr/VRDisplay.h"
 
 #include "core/css/StylePropertySet.h"
 #include "core/dom/DOMException.h"
 #include "core/dom/FrameRequestCallback.h"
 #include "core/dom/ScriptedAnimationController.h"
@@ skipping 667 matching lines @@
   context_gl_ = nullptr;
   pending_submit_frame_ = false;
   pending_previous_frame_render_ = false;
 }
 
 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_);
+  on_handled.Run(!pending_present_request_ && !is_presenting_);
 }
 
 void VRDisplay::OnDeactivate(
     device::mojom::blink::VRDisplayEventReason reason) {
   navigator_vr_->EnqueueVREvent(VRDisplayEvent::Create(
       EventTypeNames::vrdisplaydeactivate, true, false, this, reason));
 }
 
 void VRDisplay::ProcessScheduledWindowAnimations(double timestamp) {
   TRACE_EVENT1("gpu", "VRDisplay::window.rAF", "frame", vr_frame_id_);
@@ skipping 168 matching lines @@
   visitor->Trace(stage_parameters_);
   visitor->Trace(eye_parameters_left_);
   visitor->Trace(eye_parameters_right_);
   visitor->Trace(layer_);
   visitor->Trace(rendering_context_);
   visitor->Trace(scripted_animation_controller_);
   visitor->Trace(pending_present_resolvers_);
 }
 
 }  // namespace blink