Fix exiting WebVR via Android UI not fully exiting fullscreen.

device/vr/vr_device.cc

Index: device/vr/vr_device.cc
diff --git a/device/vr/vr_device.cc b/device/vr/vr_device.cc
index c580d5fff4cc3eb8dceeba35a1c7ab05b33c42cc..029f26adb4cd86b6673434ff8fd05c91929d5504 100644
--- a/device/vr/vr_device.cc
+++ b/device/vr/vr_device.cc
@@ -54,13 +54,15 @@ void VRDevice::OnDisplayChanged() {
   }
 }
 
-void VRDevice::OnExitPresent(VRServiceImpl* service) {
-  DisplayClientMap::iterator it = displays_.find(service);
+void VRDevice::OnExitPresent() {
+  DisplayClientMap::iterator it = displays_.find(presenting_service_);
   if (it != displays_.end()) {
     mojom::VRDisplayClient* client = it->second->client();
     if (client)
       client->OnExitPresent();
   }
+
+  presenting_service_ = nullptr;
 }
 
 }  // namespace device