Add an option to stress only allocations in ThreadStress.

Add an "--allocs-only" option to ART run-test 004-ThreadStress,
selecting a pre-set frequency map with allocation-related operations
only.

Also, remove an unnecessary lock object when handling option
"--locks-only".

Test: art/test/testrunner/testrunner.py -t 004-ThreadStress
Change-Id: I0c4de69667dff258a52f2f7c36b88361776dc69a
1 file changed