LayoutTest platform/mac-wk2/plugins/slow/asynchronous-plugin-initialization-multiple.html is a flaky timeout https://webkit-test-results.webkit.org/dashboards/flakiness_dashboard.html#showAllRuns=true&tests=platform%2Fmac-wk2%2Fplugins%2Fslow%2Fasynchronous-plugin-initialization-multiple.html
This test started timing out frequently on Sierra and El Capitan Release WK2 on 2/1/2017
This looks like it started with http://trac.webkit.org/r211535
Anders rolled the change out in <https://trac.webkit.org/changeset/211604>, let's see if this resolves the timeouts.
The timeouts have stopped.