Reland "Chromedriver: Make test runner emit proper test results"

This is a reland of 9b237478

Original CL was reverted just to be safe, due to https://crbug.com/855290.

There's a fix to a typo in the unexpected field; it should actually be
'is_unexpected', not 'expected'.

Original change's description:
> Chromedriver: Make test runner emit proper test results
>
> The chrome test result format needs failed tests to be marked as
> unexpected to be recognized as true failures. Otherwise they're thought
> to be acceptable failures, and don't show up as actual failures when
> parsed.
>
> Bug: 533481
> Change-Id: Ica94a18a4503a5553ef5602627643ae526155e1a
> Reviewed-on: https://chromium-review.googlesource.com/1109269
> Reviewed-by: John Chen <johnchen@chromium.org>
> Reviewed-by: Caleb Rouleau <crouleau@chromium.org>
> Commit-Queue: Stephen Martinis <martiniss@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#569341}

Bug: 533481, 855290
Change-Id: I502ace9b1f0fd97d569fe6eb6c08f660218acb01
Reviewed-on: https://chromium-review.googlesource.com/1111218Reviewed-by: Caleb Rouleau <crouleau@chromium.org>
Reviewed-by: John Chen <johnchen@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Stephen Martinis <martiniss@chromium.org>
Cr-Commit-Position: refs/heads/master@{#569770}

chrome/test/chromedriver/test/run_py_tests.py

@@ -2948,6 +2948,7 @@ if __name__ == '__main__':
 
     for failure in result.failures + result.errors:
       output['tests'][failure[0].id()]['actual'] = 'FAIL'
+      output['tests'][failure[0].id()]['is_unexpected'] = True
 
     num_fails = len(result.failures) + len(result.errors)
     output['num_failures_by_type']['FAIL'] = num_fails