[m138] Pretty print jobs.json

Cherry-pick of https://review.skia.org/1056297

Change-Id: Ie586039fda4e79cbd627720217b5de22d2f0a920
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1056356
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
2 files changed