Build: https://ci.chromium.org/p/chromium/builders/luci.chromium.try/win10_chromium_x64_rel_ng/149779

Swarming task [shard 6] passes all tests, and emits output.json but counts as a swarming failure because it failed to shut down correctly:
https://chromium-swarm.appspot.com/task?id=417ea8baeaea5a10

This in turn causes all tests to be rerun with --gtest_repeat=10, but no --gtest_filter, causing timeouts everywhere.

More detailed explanation:
The swarming failure causes the SwarmingGtestTest to be considered a failed test:
https://cs.chromium.org/chromium/build/scripts/slave/recipe_modules/test_utils/api.py?type=cs&q=scripts/slave/recipe_modules/test_utils/api.py&sq=package:chromium&g=0&l=461

However, the test results are valid and there are no failing tests. This causes tests_to_retry to return an empty list:
https://cs.chromium.org/chromium/build/scripts/slave/recipe_modules/chromium_tests/steps.py?type=cs&q=recipe_modules/chromium_tests/steps.py&sq=package:chromium&g=0&l=388

Which causes --gtest_filter to not be set:
https://cs.chromium.org/chromium/build/scripts/slave/recipe_modules/chromium_tests/steps.py?type=cs&q=recipe_modules/chromium_tests/steps.py&sq=package:chromium&g=0&l=1825

However, since the tests_to_retry is [], it fails to be caught in our earlier exit block for _test_options_for_running:
https://cs.chromium.org/chromium/build/scripts/slave/recipe_modules/chromium_tests/steps.py?type=cs&q=recipe_modules/chromium_tests/steps.py&sq=package:chromium&g=0&l=129


There are two problems to fix. 
1) We should update _test_options_for_running to also catch the empty list.
2) If test results are valid, and there are no failures, it's possible we should mark the test suite as a success even if there's an infra failure?