The regression itself was fixed in
I980aec3481a52ecc35f1811a366014a5581a7cdb, so this patch only adds a
test for it.
Also remove a comment about CachingParser failures: we don't want to
encourage people to remove it from tests anymore.
Bug: T152281
Change-Id: I3ad49050ea49bf45d3226878e091da3c8dbefdb1