There's currently no way to 
 

There's currently no way to tell when we're in the DON flow, resulting in use waiting until the current focused activity is VrCore during tests to determine if we're in the DON flow. If there's ever a way to explicitly check whether we're in the DON flow, the hack(s) in tests such as WebVrTransitionTest#testPresentationPromiseRejectedIfDonCanceled should be removed in favor of using that.