Android perf test: retry flaky tests.

There are two levels of results:
- exit_code: used to turn individual steps green / red.
- base_test_result.ResultType: useed to retry the tests.

Since some downstream tests were marked as flaky, it was no longer retrying
those tests.

BUG=301556

Review URL: https://codereview.chromium.org/25291002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226248 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226248