a bad cl candidate:
 https://chromium-review.googlesource.com/c/614310

The CL author claims that there was a BCS flake in fetching the ec blob for pyro.

Looking at the logs for that failing build nothing supports / rejects this hypothesis.

Is all the unibuild development happening on reef-uni? If so, perhaps we need a reef-uni-pre-cq to get build coverage for unibuilds before they hit CQ? Or is there already a pre-cq config with unified builds?

That CL is being tested with the following pre-cq set:
The Pre-Commit Queue has picked up your change. You can follow along at 
(nyan_blaze-no-vmtest-pre-cq) : https://luci-milo.appspot.com/buildbot/chromiumos.tryserver/no_vmtest_pre_cq/98415 
(betty-pre-cq) : https://luci-milo.appspot.com/buildbot/chromiumos.tryserver/pre_cq/50162 
(lumpy-no-vmtest-pre-cq) : https://luci-milo.appspot.com/buildbot/chromiumos.tryserver/no_vmtest_pre_cq/98421 
(samus-no-vmtest-pre-cq) : https://luci-milo.appspot.com/buildbot/chromiumos.tryserver/no_vmtest_pre_cq/98416 
(whirlwind-no-vmtest-pre-cq) : https://luci-milo.appspot.com/buildbot/chromiumos.tryserver/no_vmtest_pre_cq/98418 
(kevin-no-vmtest-pre-cq) : https://luci-milo.appspot.com/buildbot/chromiumos.tryserver/no_vmtest_pre_cq/98417 
(daisy_spring-no-vmtest-pre-cq) : https://luci-milo.appspot.com/buildbot/chromiumos.tryserver/no_vmtest_pre_cq/98414 
(cyan-no-vmtest-pre-cq) : https://luci-milo.appspot.com/buildbot/chromiumos.tryserver/no_vmtest_pre_cq/98419 
(reef-no-vmtest-pre-cq) : https://luci-milo.appspot.com/buildbot/chromiumos.tryserver/no_vmtest_pre_cq/98420 
(binhost-pre-cq) : https://luci-milo.appspot.com/buildbot/chromiumos.tryserver/pre_cq/50163  .

And nothing obviously says it's a unified build. We could convert reef-pre-cq to be reef-uni-pre-cq...

What is the pre-cq support for reef-uni at the moment? What do we have to make sure build_package errors are caught before the CQ?

impl'd in https://chromium-review.googlesource.com/c/621880

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/chromite/+/84ce4ef4ee704d0d7f68a342950360a529705bfd

commit 84ce4ef4ee704d0d7f68a342950360a529705bfd
Author: C Shapiro <shapiroc@chromium.org>
Date: Wed Aug 23 02:05:11 2017

[unibuild] Add reef-uni to the pre-cq test battery

We currently have no unified build coverage pre-cq.
This is is where a lot of work is currently taking place and it needs
the corresponding coverage.

BUG= chromium:755813 
TEST=cbuildbot --remote reef-uni-no-vmtest-pre-cq

Change-Id: I1f535a269d5f741cc2403af0bbb5ac48316b9591
Reviewed-on: https://chromium-review.googlesource.com/621880
Commit-Ready: C Shapiro <shapiroc@google.com>
Tested-by: C Shapiro <shapiroc@google.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

[modify] https://crrev.com/84ce4ef4ee704d0d7f68a342950360a529705bfd/lib/constants.py