run-perf-tests should restart DRT for each test

run-perf-tests should restart DRT for each test
https://bugs.webkit.org/show_bug.cgi?id=77506

Reviewed by Adam Barth.

Always restart DRT when running performance tests in order to minimize the dependency between tests.

* Scripts/webkitpy/layout_tests/port/chromium.py:
(ChromiumDriver.stop):
* Scripts/webkitpy/performance_tests/perftestsrunner.py:
(PerfTestsRunner._run_tests_set):
(PerfTestsRunner._run_single_test):
* Scripts/webkitpy/performance_tests/perftestsrunner_unittest.py:
(create_runner):
(test_run_passing_test):
(test_run_silent_test):
(test_run_failed_test):
(test_run_tonguey_test):
(test_run_timeout_test):
(test_run_crash_test):
(test_run_test_set_kills_drt_per_run):
(test_run_test_set_kills_drt_per_run.TestDriverWithStopCount):
(test_run_test_set_kills_drt_per_run.TestDriverWithStopCount.__init__):
(test_run_test_set_kills_drt_per_run.TestDriverWithStopCount.stop):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@106442 268f45cc-cd09-0410-ab3c-d52691b4dbfc