GitLab

Add more detailed reason "invalid JSON" why the parsing failed.

Bug: 834245
Change-Id: I9a81f425a2d877fecab7a9da1176e043e154d3f6
Reviewed-on: https://chromium-review.googlesource.com/c/1329977Reviewed-by: Lutz Justen <ljusten@chromium.org>
Commit-Queue: Alexander Hendrich <hendrich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#607565}