This will start to collect engine benchmarks in the flutter-cirrus
Datastore for all post-submit commits.
We're using this to test how https://github.com/liyuqian/metrics_center
works. Once it's stablized, we should move metrics_center into
flutter/packages, and migrate data to flutter-infra Datastore.
Related issue: https://github.com/flutter/flutter/issues/37434
