[bazel] Make use of gcs_mirror_url()

Change-Id: I29ce3eadcc89f6dd7890dc45c279dce032400989
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/739857
Reviewed-by: Leandro Lovisolo <lovisolo@google.com>
Commit-Queue: Kevin Lubick <kjlubick@google.com>
Auto-Submit: Kevin Lubick <kjlubick@google.com>
Commit-Queue: Leandro Lovisolo <lovisolo@google.com>
2 files changed