This makes the library behave more like what we'd expect,
while still allowing certain function to specify that
returning 204 or 404 is expected/acceptable behavior.

Change-Id: If3ce5598d1603819ee97aaeab0072a9e786ed96d
Reviewed-on: https://chromium-review.googlesource.com/481043Reviewed-by: Robbie Iannucci <iannucci@chromium.org>
Commit-Queue: Aaron Gable <agable@chromium.org>