The status FAILED and BAILED_OUT only distinguishes between whether an
exception is pending or not. Such a distinction is obsolete by now as
all callers check for pending exceptions directly. Also it is impossible
for any concurrent part of the job to actually set a pending exception,
hence even the assertion that the concurrent part does not return FAILED
is obsolete.

R=bmeurer@chromium.org

Review-Url: https://codereview.chromium.org/1926693003
Cr-Commit-Position: refs/heads/master@{#35834}