GitLab

Problem: EXPECT_EQ(1U, task_source->HasOneRef()) fails because threads don't
release ref right away.
Fix: use JoinForTesting

Bug: 1011502
Change-Id: I4f5c7da2d3cf66cd6635a97c4b99acba866c2db3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1845232
Commit-Queue: François Doray <fdoray@chromium.org>
Reviewed-by: François Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/master@{#703689}