This is probably not a Findit bug but I'm not sure who to assign the owner to.

It seems during gtest result collection a non-ascii character is present cauging json parsing to fail and leading to the exception:

exit code (as seen by runtest.py): 1
@@@STEP_LOG_LINE@FetcherPoolTest.AddNullURLFetcher@FetcherPoolTest.AddNullURLFetcher (run #1):@@@
@@@STEP_LINK@logdog-->FetcherPoolTest.AddNullURLFetcher@https://luci-logdog.appspot.com/v/?s=bb%2Ftryserver.chromium.win%2Fwin_chromium_variable_gn%2F10%2F%2B%2Frecipes%2Fsteps%2Ftest_06226c0e27690074422702e0a57b717eea7b361f.components_unittests__06226c0e27690074422702e0a57b717eea7b361f__on_Windows-7-SP1%2F0%2Flogs%2FFetcherPoolTest.AddNullURLFetcher%2F0@@@
@@@STEP_LOG_LINE@FetcherPoolTest.AddNullURLFetcher@[ RUN      ] FetcherPoolTest.AddNullURLFetcher@@@
@@@STEP_LOG_LINE@FetcherPoolTest.AddNullURLFetcher@e:uild\slave\win_gnuild\src\components\precache\coreetcher_pool_unittest.cc(163): error: Death test: { pool.Add(std::move(null_ptr)); }@@@
@@@STEP_LOG_LINE@FetcherPoolTest.AddNullURLFetcher@    Result: failed to die.@@@
@@@STEP_LOG_LINE@FetcherPoolTest.AddNullURLFetcher@ Error msg:@@@
@@@STEP_WARNINGS@@@
failed to process gtest output JSON
@@@STEP_LOG_LINE@failed to process gtest output JSON@Traceback (most recent call last):@@@
@@@STEP_LINK@logdog-->failed to process gtest output JSON@https://luci-logdog.appspot.com/v/?s=bb%2Ftryserver.chromium.win%2Fwin_chromium_variable_gn%2F10%2F%2B%2Frecipes%2Fsteps%2Ftest_06226c0e27690074422702e0a57b717eea7b361f.components_unittests__06226c0e27690074422702e0a57b717eea7b361f__on_Windows-7-SP1%2F0%2Flogs%2Ffailed_to_process_gtest_output_JSON%2F0@@@
@@@STEP_LOG_LINE@failed to process gtest output JSON@  File "E:\b\build\scripts/slave\recipe_modules\swarming\resources\collect_gtest_task.py", line 184, in main@@@
@@@STEP_LOG_LINE@failed to process gtest output JSON@    emit_test_annotations(exit_code, merged)@@@
@@@STEP_LOG_LINE@failed to process gtest output JSON@  File "E:\b\build\scripts/slave\recipe_modules\swarming\resources\collect_gtest_task.py", line 127, in emit_test_annotations@@@
@@@STEP_LOG_LINE@failed to process gtest output JSON@    annotation_utils.annotate('', exit_code, parser)@@@
@@@STEP_LOG_LINE@failed to process gtest output JSON@  File "E:\b\build\scripts\slave\annotation_utils.py", line 88, in annotate@@@
@@@STEP_LOG_LINE@failed to process gtest output JSON@    log_processor.FailureDescription(failure))@@@
@@@STEP_LOG_LINE@failed to process gtest output JSON@  File "E:\b\build\scripts\slave\slave_utils.py", line 703, in WriteLogLines@@@
@@@STEP_LOG_LINE@failed to process gtest output JSON@    print '@@@STEP_LOG_LINE@%s@%s@@@' % (logname, line)@@@
@@@STEP_LOG_LINE@failed to process gtest output JSON@UnicodeDecodeError: 'ascii' codec can't decode byte 0x81 in position 134: ordinal not in range(128)@@@
@@@STEP_LOG_LINE@failed to process gtest output JSON@@@@
@@@STEP_LOG_END@failed to process gtest output JSON@@@
@@@STEP_CURSOR@test 06226c0e27690074422702e0a57b717eea7b361f.components_unittests (06226c0e27690074422702e0a57b717eea7b361f) on Windows-7-SP1@@@

The following Findit try jobs ended with such error:
https://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_variable/builds/194
https://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_variable_gn/builds/10