This test is flaky and fails once every ~20 runs on WebKit Linux Trusty (dbg):
https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=webkit_layout_tests&tests=rootscroller%2Fgesture-scroll-document-not-root-scroller.html

It just flaked on one of my patches:
https://ci.chromium.org/buildbot/tryserver.chromium.linux/linux_layout_tests_slimming_paint_v2/11302