From what I can tell, this is already fixed at trunk (310749).

Broke somewhere in 309984:310535, was fixed somewhere in 310580:310749

Fix was 310662, a revert of 310457.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0c7513e4c72d3d95cfe9c6608492be0b62c7973b

commit 0c7513e4c72d3d95cfe9c6608492be0b62c7973b
Author: Nico Weber <thakis@chromium.org>
Date: Fri Aug 11 20:56:55 2017

Explicitly run ios-device trybot on clang rolls.

https://chromium-review.googlesource.com/c/587422 removed that bot from
the default cq set, leading to us landing a clang roll that broke
ios-device builds on the main waterfall.

Bug: 740301, 754829 
Change-Id: I0263999cdd5a5831ae562280bd0f79b9f4eda325
Reviewed-on: https://chromium-review.googlesource.com/612432
Reviewed-by: Hans Wennborg <hans@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#493848}
[modify] https://crrev.com/0c7513e4c72d3d95cfe9c6608492be0b62c7973b/docs/updating_clang.md

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/7792c9b88e70e8362ee70e205b4d32b5f00110e4

commit 7792c9b88e70e8362ee70e205b4d32b5f00110e4
Author: Justin Cohen <justincohen@google.com>
Date: Fri Aug 11 20:57:50 2017

Also build ClangToTiOS in arm64, x86, x64

Bug:  754829 
Change-Id: I0ce2cde9b812de65006209db3cd56f70be82cc1a
Reviewed-on: https://chromium-review.googlesource.com/612427
Commit-Queue: Justin Cohen <justincohen@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Mike Baxley <baxley@chromium.org>
Cr-Commit-Position: refs/heads/master@{#493849}
[modify] https://crrev.com/7792c9b88e70e8362ee70e205b4d32b5f00110e4/ios/build/bots/chromium.fyi/ClangToTiOS.json

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/6ff639aa128c9412ff5d665519284301a7bfceab

commit 6ff639aa128c9412ff5d665519284301a7bfceab
Author: Nico Weber <thakis@chromium.org>
Date: Fri Aug 11 21:04:50 2017

Email cq config changes to cq-config-changes@chromium.org

Also fix the addresses of goma team members to end in @chromium.org
instead of chromium.com

Bug:  754829 
Change-Id: I16107014c49581a46ae804ae8e9b27cf612e3d52
Reviewed-on: https://chromium-review.googlesource.com/612433
Reviewed-by: Hans Wennborg <hans@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#493855}
[modify] https://crrev.com/6ff639aa128c9412ff5d665519284301a7bfceab/WATCHLISTS

We reverted the roll and rolled to a newer revision with a fix.