[infra] Add service_account_json option to asset utils

Change-Id: If2686949009ba6fdf703ea794c0764c0e9966590
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/252261
Auto-Submit: Ben Wagner aka dogben <benjaminwagner@google.com>
Reviewed-by: Eric Boren <borenet@google.com>
Commit-Queue: Ben Wagner aka dogben <benjaminwagner@google.com>
2 files changed