Set up ANGLE shadow buckets Sets up ANGLE shadow buckets so that LED jobs can be triggered now that real builds are the only supported path. This was effectively copied from Chromium's configuration but with the relevant pools, service accounts, etc. swapped out for ANGLE ones. Bug: chromium:353904289 Change-Id: Idd958faf73d9d62180151f4a72817fb1543f208f Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/5723088 Commit-Queue: Yuly Novikov <ynovikov@chromium.org> Reviewed-by: Chan Li <chanli@chromium.org> Reviewed-by: Yuly Novikov <ynovikov@chromium.org>