There are situations where the WebVR application may end up in an unrecoverable broken state. In this case, we currently continue displaying the last-submitted frame, including reprojection where applicable, or a blank black frame if none were ever submitted successfully.

(See also issue 716071 about underperforming applications, including transient issues that aren't known to be unrecoverable.)

If it's possible to detect these situations programatically, we should handle them by reporting the error to the user and/or automatically exiting presentation.

Examples can include:

- application fails to call vrDisplay.requestAnimationFrame from within the current rAF callback, so there will not be any further frames being generated. In theory an application may do something odd such as calling vrDisplay.rAF from a future scheduled setTimeout, that would be hard to detect. If that's a concern, clarify the spec to indicate it's not legal?

- canvas resized to an invalid size such as 0x0 pixels, or a too-large size where resizing failed