Fix data race in trybot ingestion
Fix data race in trybot ingestion

BUG=skia:

Change-Id: Ic10f7b5b792c3db93c8757a932b8b1f2dde6e778
Reviewed-on: https://skia-review.googlesource.com/3420
Reviewed-by: Ravi Mistry <9fa2e7438b8cb730f96b74865492597170561628@google.com>
Commit-Queue: Stephan Altmueller <43343ec95731c0e8daa7359daf7f2f3935582b24@google.com>

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot