1. If notifyTestComplete is called before the first paint,
give a clear assert instead of a confusing crash.
2. Add runAfterDisplay. This is a copy of the equivalent
file in Blink. Avoids the incorrect 100ms setTimeout. I had
thought there was a deeper bug here, but it appears to just
be the issue from #1 now that we properly pump frames
in testing mode by using a face Surfaces application.
R=abarth@chromium.org
Review URL: https://codereview.chromium.org/826343003