Fix race in cleanup test
Fix race in cleanup test

Bug: skia:7206
Change-Id: Iacd9facfe0259dfaa6d16a8f12c940c8710950be
Reviewed-on: https://skia-review.googlesource.com/70580
Commit-Queue: Eric Boren <0e499112533c8544f0505ea0d08394fb5ad7d8fa@google.com>
Reviewed-by: Kevin Lubick <7cdab2cfab351f23814786ba39716e90eed69047@google.com>

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