Add a stress test for notifyStartupCompleted

Call notifyStartupCompleted to stress test the freeing logic for
race conditions. This is done while dex files and app images are
being loaded from another thread.

Test: test/run-test --host 1002
Bug: 135486422

Change-Id: I138586d83db7bc2f8d75f223170f9bf4af5e71eb
4 files changed