Revert "Change error callback to log error"

This reverts commit 973eb033820a688aa0aa10160736924bc1fdf13c.

Reason for revert: Test became flaky with this CL: crbug.com/860647

Original change's description:
> Change error callback to log error
> 
> This callback was just ignoring the error creating an empty result, this
> CL changes to log error so it can be identified and fixed.
> 
> Cq-Include-Trybots: luci.chromium.try:closure_compilation
> Change-Id: I85c2c4de71742a2d438e30fe75f531750345dc4f
> Reviewed-on: https://chromium-review.googlesource.com/1125699
> Commit-Queue: Sasha Morrissey <sashab@chromium.org>
> Reviewed-by: Sasha Morrissey <sashab@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#572875}

TBR=sashab@chromium.org,lucmult@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: I132067f04aef9055e35678835f703ca51702faf9
Cq-Include-Trybots: luci.chromium.try:closure_compilation
But: 860647
Reviewed-on: https://chromium-review.googlesource.com/1128639
Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
Reviewed-by: Noel Gordon <noel@chromium.org>
Reviewed-by: Sasha Morrissey <sashab@chromium.org>
Commit-Queue: Luciano Pacheco <lucmult@chromium.org>
Cr-Commit-Position: refs/heads/master@{#573210}
1 file changed