V8 uses a Buildbot builder that builds for every revision and then triggers another builder (aka tester) that runs tests. Since tester take significantly longer we can only run tests every few revisions or so.

In LUCI world this does not work because each triggered build is added to buildbucket and buildbucket requests are not merged, hence we'll quickly run out of tester capacity. We need a feature that would allow merging multiple build requests.

This is blocking V8's migration to LUCI.