This is looking green in recent builds, but it looks like the setup_properties has a history of occasionally failing on this bot (20 failures in last 200 builds).  This failure also looks similar to the one on official builders in issue 638988.  Adding troopers to take a look.

Sample failure log:

Traceback (most recent call last):
  File "../../../scripts/slave/annotated_run.py", line 340, in <module>
    sys.exit(shell_main(sys.argv))
  File "../../../scripts/slave/annotated_run.py", line 335, in shell_main
    return main(argv[1:])
  File "../../../scripts/slave/annotated_run.py", line 315, in main
    tdir, opts.build_properties, use_factory_properties_from_disk)
  File "../../../scripts/slave/annotated_run.py", line 101, in get_recipe_properties
    workdir, mastername, buildername)
  File "../../../scripts/slave/annotated_run.py", line 165, in get_factory_properties_from_disk
    dump_cmd, env.Build, proc.returncode, out, err))
LookupError: Failed to get the master config; running ['/usr/bin/python', '/b/build/scripts/tools/dump_master_cfg.py', '/b/build/masters/master.tryserver.chromium.mac', '/b/build/slave/ios-device/.recipe_runtime/tmpMgiuV8/dump_master_cfg.json'] in '/b/build' returned exit code 1
stdout: 
stderr: error while parsing /b/build/masters/master.tryserver.chromium.mac/master.cfg: 
Traceback (most recent call last):
  File "/b/build/scripts/common/master_cfg_utils.py", line 105, in LoadConfig
    localdict = ExecuteConfig(canonical_config)
  File "/b/build/scripts/common/master_cfg_utils.py", line 80, in ExecuteConfig
    exec f in localDict
  File "/b/build/masters/master.tryserver.chromium.mac/master.cfg", line 16, in <module>
    from master import master_utils
  File "/b/build/scripts/master/master_utils.py", line 24, in <module>
    from buildbot.status.web.baseweb import WebStatus
  File "/b/build/third_party/buildbot_8_4p1/buildbot/status/web/baseweb.py", line 46, in <module>
    from infra_libs.ts_mon.common import http_metrics
ImportError: No module named infra_libs.ts_mon.common

Traceback (most recent call last):
  File "/b/build/scripts/tools/dump_master_cfg.py", line 55, in <module>
    sys.exit(main(sys.argv[1:]))
  File "/b/build/scripts/tools/dump_master_cfg.py", line 47, in main
    json.dump(result['BuildmasterConfig'],
TypeError: 'NoneType' object has no attribute '__getitem__'

Hey Sergey, is the ts_mon error a problem here or is it a red herring for something else?

This was likely due to dsansome@'s recent attempts to land infra_libs & ts_mon into build.git. AFAIK, the change was reverted, and I don't yet know if it re-landed again. 
+dsansome for more info.

Yeah this was me, it's fixed with https://codereview.chromium.org/2256183003/

Issue 638988 has been merged into this issue.