The CL had the request for the bot in it apparently:

Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel;master.tryserver.chromium.linux:linux_chromium_dbg_ng;master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2

Something added it there. Removing it makes progress.

I'll mark this is WontFix, since everything appears working as expected: specifying a missing builder in Cq-Include-Trybots will make the CQ run fail. 

I'm not sure how Cq-Include-Trybots ended up in the CL description, but it's unlikely to be an issue with the service (it doesn't touch the commit messages).

PRESUBMIT.py of directories in which CL modified files has added that line. The problem is that linux_chromium_dbg_ng has migrated to luci, so it should be loaded from luci.chromium.try:linux_chromium_dbg_ng

Thank you, build/PRESUBMIT.py has

build/PRESUBMIT.py:24:      'master.tryserver.chromium.linux:linux_chromium_dbg_ng',

I will convert it.

tandrii is fixing with a CL :)

Phew, https://chromium-review.googlesource.com/c/chromium/src/+/1044772

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f3dd93a5c5289a738877b86ed90f1ef9a24ffbf1

commit f3dd93a5c5289a738877b86ed90f1ef9a24ffbf1
Author: Andrii Shyshkalov <tandrii@chromium.org>
Date: Fri May 04 21:12:43 2018

Fix buildbot linux_chromium_dbg_ng reference in PRESUBMIT.

Build has migrated to LUCI.

R=danakj@chromium.org

Bug:  839600 
Change-Id: I15fab6330a0215b4edf14318993ae4608d269dbe
Reviewed-on: https://chromium-review.googlesource.com/1044772
Reviewed-by: danakj <danakj@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Commit-Queue: Andrii Shyshkalov <tandrii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#556191}
[modify] https://crrev.com/f3dd93a5c5289a738877b86ed90f1ef9a24ffbf1/build/PRESUBMIT.py