We have to ensure that replacements do not have replacements because
otherwise a changed replacement (of the replacement) wouldn't trigger
graph revisitations. However, this invariant can be temporarily
violated when the information propagated along the effect chain is
outdated for another reason. So we should only check this for the final
fixed-point.


Bug: chromium:787959

Change-Id: I4a6b2c4f6ff3205649c0f866654900d4ab126acf
Reviewed-on: https://chromium-review.googlesource.com/817777Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49995}