The test harness wasn't waiting on `CliAppFixture.onAppStarted` which
could cause an unhandled exception if the test cleanup started before
the target application finished initializing. This typically only
occurred while the test was running on a machine under load.
Fixes https://github.com/dart-lang/sdk/issues/48669
TEST=Locally while running under load (e.g., `stress -c 72`)
Change-Id: Ieb67e46f62c33101490899440574fb57fc0f8882
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/238922
Reviewed-by: Kenzie Davisson <kenzieschmoll@google.com>
Commit-Queue: Ben Konyi <bkonyi@google.com>
Ben Konyi
0950d887be