Reland "[gold] Add logging to diff"
Reland "[gold] Add logging to diff"

This is a reland of adad227afe4ad4f3df81d1737bc6eab8f5c94595

Original change's description:
> [gold] Add logging to diff
>
> Change-Id: If307447f9f2f6a28fb78769acc5443a22a2ac402
> Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/443404
> Reviewed-by: Ravi Mistry <rmistry@google.com>

Change-Id: I1a56a8343095c8851b9f37179b9ab5905c39fb63
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/443617
Bot-Commit: Rubber Stamper <d516c4cc2192058ab8dae3d306acbdaf2ce6574f@appspot.gserviceaccount.com>

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot