run-perf-tests reports wrong commit time
https://bugs.webkit.org/show_bug.cgi?id=110746

Reviewed by Andreas Kling.

The bug was caused by running "svn info" on a subdirectory, which returns a timestamp
of when the subdirectory was last modified.

Run "svn info -r <revision> <repository root>" instead. Specifying revision number is
insufficient since running "svn log -r <revision>" on a partial checkout only returns
an empty result if the revision didn't modify the subdirectory.

For git, there is no partial checkout, so we just need to pass in "-r" option to keep
the interface compatible with svn.

* Scripts/webkitpy/common/checkout/scm/git.py:
(Git.timestamp_of_latest_commit):
* Scripts/webkitpy/common/checkout/scm/scm.py:
(SCM.timestamp_of_latest_commit):
* Scripts/webkitpy/common/checkout/scm/scm_mock.py:
(MockSCM.timestamp_of_latest_commit):
* Scripts/webkitpy/common/checkout/scm/scm_unittest.py:
(test_timestamp_of_latest_commit):
* Scripts/webkitpy/common/checkout/scm/svn.py:
(SVN.timestamp_of_latest_commit):
* Scripts/webkitpy/performance_tests/perftestsrunner.py:
(PerfTestsRunner._generate_results_dict):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@143903 268f45cc-cd09-0410-ab3c-d52691b4dbfc