What happened here was that I ran webkit-patch rebaseline-cl which downloaded an incorrect new baseline :-/ A baseline for fast/text/international/thai-line-breaks.html shouldn't have been in that CL.
Specifically, this is because in this try job: https://build.chromium.org/p/tryserver.blink/builders/win10_blink_rel/builds/650 thai-line-breaks.html failed both with and without patch; rebaseline-cl should have ignored tests that fail with patch. This is bug 642980 .
Comment 1 by bugdroid1@chromium.org
, Sep 8 2016