This is part of WPT Export 2.0 (issue 707006)
In bug 686471 we started supporting merging all in-flight PRs at once, but the exporter still enforces only 1 in-flight PR at a time. The next step is to start creating as many PRs as there are exportable commits.
Comment 1 by jeffcarp@chromium.org
, Mar 18 2017