It reproduces with pinned Clang too. It stops reproducing if I drop is_official_build = true.

Seems familiar :-)

I see Nico already noticed this :-)
https://chromium-review.googlesource.com/c/chromium/src/+/999481#message-55b3bc8fe8857b23f45b8687719c408b1cc66e14

Removing the expectations string here: https://chromium-review.googlesource.com/#/c/chromium/src/+/1006582

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/93e76e38c34fab55bc9f19ba50ced5cc0b4f919e

commit 93e76e38c34fab55bc9f19ba50ced5cc0b4f919e
Author: Hans Wennborg <hans@chromium.org>
Date: Wed Apr 11 09:20:29 2018

Fix U2fParsingUtils.AppendSelfCrashes in official builds

Official builds remove the strings passed to CHECKs, causing the
expected string to not show up and breaking this test.

Removing the expectation strings to unbreak the test for now. As Nico
commented on https://crrev.com/c/999481 perhaps a better fix would be
to not use a death test at all.

TBR=jdoerrie

Bug:  831494 
Change-Id: Ic9e2ca4cfe4f5f05d47c00fb4727ea37d6fadcfc
Reviewed-on: https://chromium-review.googlesource.com/1006582
Reviewed-by: Hans Wennborg <hans@chromium.org>
Commit-Queue: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549837}
[modify] https://crrev.com/93e76e38c34fab55bc9f19ba50ced5cc0b4f919e/device/fido/u2f_parsing_utils_unittest.cc

Thanks for the quick fix, apologies for breaking the build.