Favro card: https://favro.com/card/c564ede4ed3337f7b17986b6/Uni-39669

If you plug in a MR HMD in while a standalone app is running the app while pause and the MR portal will render the app. However performance will drop from an error spamming the output log about tracking in a D3D app.

Notes:
Acer
D3D = Repro the bug
XAML = The app terminates on initialization

Repro Steps:
1.) Open a MR project
-Requires D3D
-Turn off Full screen (User view)
2.) Disconnect MR HMD
3.) Have MR portal open and waiting for the device
4.) Build the UWP MR app
5.) Open the VS sln and launch the app
6.) Observe the Desktop flat app
7.) Plug in the MR HMD
8.) Observe the MR portal Windows
9.) Activate the presence sensor

Actual:
Apps are not handling starting a MR app without a HMD plugged in, then having a HMD plugged in.

Couldn't find spatial stage - we have to track as though we were stationary for our tracking space type, even though we should be at room-scale!

(Filename: C:\buildslave\unity\build\Runtime/VR/HoloLens/HoloLensWorldManager.cpp Line: 219)