fast/dom/shadow/gc-shadow-expected.txt seems to be failing intermittently on Chromium Linux after the fix for 59571. See for example http://build.chromium.org/p/chromium.webkit/builders/Webkit%20Linux%2064/builds/3286 . Suppressing this failure for the moment.
I am closing this because I removed the flakiness expectation in r86518 and the test has apparently been running reliably since then.