The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/tools/build/+/fe5829ec8ac2056465230d88fdcd6fb7dd8498d5

commit fe5829ec8ac2056465230d88fdcd6fb7dd8498d5
Author: Chan <chanli@chromium.org>
Date: Mon Jun 11 20:21:29 2018

Fix a bug when getting pass_fail_count from an invalid test results.

Sample failed build:https://ci.chromium.org/p/chromium/builders/luci.chromium.findit/findit_variable/3193。
Many swarming tasks failed with no or empty test results. And then when getting pass_fail_counts, since only the existence of the suffix as key was checked but not the test_result, we may end up doing None.pass_fail_counts or {}.pass_fail_counts which is not desirable.

Bug:  849901 
Change-Id: I11e72b0395da097ed3d1052a79dabfeaed33b889
Reviewed-on: https://chromium-review.googlesource.com/1087930
Commit-Queue: Chan Li <chanli@chromium.org>
Reviewed-by: John Budorick <jbudorick@chromium.org>
Reviewed-by: Roberto Carrillo <robertocn@chromium.org>

[modify] https://crrev.com/fe5829ec8ac2056465230d88fdcd6fb7dd8498d5/scripts/slave/recipe_modules/chromium_tests/tests/steps/swarming_isolated_script_test.expected/histograms_LUCI_missing_perf_dashboard_machine_group_property.json
[delete] https://crrev.com/492c43ddfa2e783c723f59e54e2c9f5feb8e79de/scripts/slave/recipe_modules/chromium_tests/tests/steps/swarming_isolated_script_test.expected/customized_test_options.json
[delete] https://crrev.com/492c43ddfa2e783c723f59e54e2c9f5feb8e79de/scripts/slave/recipe_modules/chromium_tests/tests/steps/local_isolated_script_test.expected/log_pass_fail_counts.json
[modify] https://crrev.com/fe5829ec8ac2056465230d88fdcd6fb7dd8498d5/scripts/slave/recipe_modules/chromium_tests/tests/steps/swarming_isolated_script_test.expected/chartjson_no_results_failure.json
[modify] https://crrev.com/fe5829ec8ac2056465230d88fdcd6fb7dd8498d5/scripts/slave/recipe_modules/chromium_tests/tests/steps/swarming_isolated_script_test.expected/chartjson_invalid.json
[modify] https://crrev.com/fe5829ec8ac2056465230d88fdcd6fb7dd8498d5/scripts/slave/recipe_modules/chromium_tests/tests/steps/swarming_gtest_test.py
[modify] https://crrev.com/fe5829ec8ac2056465230d88fdcd6fb7dd8498d5/scripts/slave/README.recipes.md
[modify] https://crrev.com/fe5829ec8ac2056465230d88fdcd6fb7dd8498d5/scripts/slave/recipe_modules/chromium_tests/tests/steps/local_isolated_script_test.py
[modify] https://crrev.com/fe5829ec8ac2056465230d88fdcd6fb7dd8498d5/scripts/slave/recipe_modules/chromium_tests/tests/steps/local_gtest_test.expected/android.json
[modify] https://crrev.com/fe5829ec8ac2056465230d88fdcd6fb7dd8498d5/scripts/slave/recipe_modules/chromium_tests/tests/steps/swarming_gtest_test.expected/overrides.json
[modify] https://crrev.com/fe5829ec8ac2056465230d88fdcd6fb7dd8498d5/scripts/slave/recipe_modules/chromium_tests/steps.py
[modify] https://crrev.com/fe5829ec8ac2056465230d88fdcd6fb7dd8498d5/scripts/slave/recipe_modules/chromium_tests/tests/steps/swarming_gtest_test.expected/no_result_json.json
[modify] https://crrev.com/fe5829ec8ac2056465230d88fdcd6fb7dd8498d5/scripts/slave/recipe_modules/chromium_tests/tests/steps/swarming_isolated_script_test.expected/chartjson_max_failures.json
[modify] https://crrev.com/fe5829ec8ac2056465230d88fdcd6fb7dd8498d5/scripts/slave/recipes/findit/chromium/test.py
[modify] https://crrev.com/fe5829ec8ac2056465230d88fdcd6fb7dd8498d5/scripts/slave/recipe_modules/chromium_tests/tests/steps/local_gtest_test.expected/basic.json
[modify] https://crrev.com/fe5829ec8ac2056465230d88fdcd6fb7dd8498d5/scripts/slave/recipe_modules/chromium_tests/tests/steps/swarming_isolated_script_test.py

The change should make sure try jobs don't fail because of lacking pass_fail_counts. There is another bug to fix the root cause of invalid test_results at 851685.