Teardown logic introduced in ag/16247901 is called on a foreground
thread in ActvitiyManager. The teardown itself might be time-consuming,
causing system_server to crash due to a blocked foreground thread (see
linked bug for more context).
This CL limits the scope of the fix to just the new logic that caused
the regression. Follow-up improvements should be made to ensure
time-consuming operations don't block foreground threads in the future
(b/242307900 will track).
Fixes: 213860448
Test: 1. atest UserBackupManagerServiceTest
2. atest CtsBackupTestCases
3. Kill app during full backup -> ensure agent is properly torn
down.
4. Modify BackupTransport::cancelFullBackup() impl. to block; kill
app during full backup -> ensure foreground thread is not
blocked and agent is still properly torn down.
Change-Id: I6c1cb1ff71814564d5884a362135edfad3b258f2
c88bdf8a75