Currently when we schedule a frame we check if the frame and document are still present. We should ensure and make clear that the document is destructed in such an way that we should never schedule a frame without a document, and remove this check. 

https://cs.chromium.org/chromium/src/third_party/blink/renderer/modules/xr/xr_frame_provider.cc?type=cs&sq=package:chromium&g=0&l=223