We've had several breaks where Chrome behavior changes/bugs break the polyfill, and we don't realize until close to shipping.

We should test the polyfill on recent pre-stable Chrome to find and address issues earlier.

Example areas to look at:
* generic sensors, fallback
* device motion
* xr over vr, vr over xr
* rendering/canvas
* iframes, focus, cross-origin/same-origin, feature policy, oopif?

Could automate or do manual.