run-perf-tests should timeout sooner

run-perf-tests should timeout sooner
https://bugs.webkit.org/show_bug.cgi?id=77026

Reviewed by Adam Barth.

Bump off the timeout from 10 minutes to 4 minutes.

Also use float instead of str in test result values to compress the size of json files bots upload.

* Scripts/webkitpy/performance_tests/perftestsrunner.py:
(PerfTestsRunner._parse_args):
(PerfTestsRunner._process_chromium_style_test_result):
(PerfTestsRunner._process_parser_test_result):
* Scripts/webkitpy/performance_tests/perftestsrunner_unittest.py:
(test_run_test_set_for_parser_tests):
(test_run_test_set_with_json_output):
(test_run_test_set_with_json_source):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@105915 268f45cc-cd09-0410-ab3c-d52691b4dbfc