huangml@ could you PTAL. You can also re-assign if this is not something you should do.

Seems like the build*-m9 pool bots are all macOS10.13.  The bots are all inside "chrome" swarming pool,  I don't know if there is an easy way to assign tasks to specific OS versions for swarming.  +Sergey who may know more about it.

See also issue 782033.

Technically, we can specify dimension os:Mac-10.12 in the triggering recipe instead of just "Mac", but this reduces the available pool by almost half, and will require recipe change (rather than just build config) when we upgrade the bots. Maybe it's OK in the short term, and if only done for ios bots.

Merged into issue 782033 as the test is now disabled on iOS.

Re-open the bug as we'd prefer to have the test coverage back on.

I'm not sure about the timeline when 10.13 will be available for corp or whether the test can be fixed before that.  Uploaded a potential workaround in iOS recipe to allow test run on mac10.12 only.
https://chromium-review.googlesource.com/c/chromium/tools/build/+/775361

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/tools/build/+/7b37da63c63ae8a2b5fcc3b4e943c8145a32c28d

commit 7b37da63c63ae8a2b5fcc3b4e943c8145a32c28d
Author: Menglu Huang <huangml@chromium.org>
Date: Thu Nov 16 23:20:29 2017

Add a flag in recipe to allow tests run on passed-in MacOS version.

We have some tests failing on macOS-10.13,  which is not ready for corp
machines yet. Developers cannot fix the test until that happens.  Add a
workaround in iOS recipe to allow tests run on passed-in MacOS version
machines for iOS simulator tests.

The workaround will allow tests to pass in a macOS version flag in the
configuration file for simulators:
{
  "app": "chrome_test",
  "host os": "Mac-10.12",
  "device type": "iPhone 7",
  "os": "11.0"
}
Bug:785185
Change-Id: I475e35e12f90ff4bb1fe7cd5d8f40dabf3de87c9
Reviewed-on: https://chromium-review.googlesource.com/775361
Commit-Queue: Menglu Huang <huangml@chromium.org>
Reviewed-by: smut <smut@google.com>

[modify] https://crrev.com/7b37da63c63ae8a2b5fcc3b4e943c8145a32c28d/scripts/slave/recipe_modules/ios/api.py
[modify] https://crrev.com/7b37da63c63ae8a2b5fcc3b4e943c8145a32c28d/scripts/slave/recipe_modules/ios/examples/full.expected/basic.json
[modify] https://crrev.com/7b37da63c63ae8a2b5fcc3b4e943c8145a32c28d/scripts/slave/recipe_modules/ios/examples/full.py

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/52b96e7e1578bba73f2b1702eeb49fa98ec8fd9a

commit 52b96e7e1578bba73f2b1702eeb49fa98ec8fd9a
Author: Menglu Huang <huangml@chromium.org>
Date: Fri Nov 17 19:29:56 2017

Do not run iOS base_unittests on macOS 10.13

Bug:  785185 
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet;master.tryserver.chromium.mac:ios-simulator-full-configs
Change-Id: I7b432dc42efca64870effc7ff819a8036bb649da
Reviewed-on: https://chromium-review.googlesource.com/775792
Reviewed-by: Sylvain Defresne <sdefresne@chromium.org>
Commit-Queue: Menglu Huang <huangml@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517512}
[modify] https://crrev.com/52b96e7e1578bba73f2b1702eeb49fa98ec8fd9a/ios/build/bots/tests/screen_size_dependent_tests.json