Fix potential race conditions with wait groups
Fix potential race conditions with wait groups

git grep says these were the only places affected.

Thanks to https://skia-review.googlesource.com/c/buildbot/+/66503
for pointing the first of these out.

Bug: skia:
Change-Id: I51b4a1018bee6dbaab04be1be298e97079421255
Reviewed-on: https://skia-review.googlesource.com/66740
Reviewed-by: Stephan Altmueller <43343ec95731c0e8daa7359daf7f2f3935582b24@google.com>
Commit-Queue: Kevin Lubick <7cdab2cfab351f23814786ba39716e90eed69047@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