system_health.memory_mobile (and possibly other tests) fail to upload test results with the following error:

Input JSON file probably has full json results format
Uploading JSON files for builder "Memory Infra Tester" to server "test-results.appspot.com"
INFO:root:Sending request to https://test-results.appspot.com/testfile/upload at 2017-08-02 06:50:03.771241 UTC
Traceback (most recent call last):
  File "/b/rr/tmpUqrcL7/rw/checkout/scripts/slave/recipe_modules/test_results/resources/upload_test_results.py", line 200, in <module>
    sys.exit(main(sys.argv[1:]))
  File "/b/rr/tmpUqrcL7/rw/checkout/scripts/slave/recipe_modules/test_results/resources/upload_test_results.py", line 195, in main
    options.test_results_server, attrs, files, 120)
  File "/b/rr/tmpUqrcL7/rw/checkout/scripts/slave/recipe_modules/test_results/resources/test_results_uploader.py", line 51, in upload_test_results
    timeout_secs)
  File "/b/rr/tmpUqrcL7/rw/checkout/scripts/slave/recipe_modules/test_results/resources/test_results_uploader.py", line 135, in _retry_exp_backoff
    % (e.code, e.filename, e.read()))
test_results_uploader.PermanentError: Received HTTP status 400 loading "https://test-results.appspot.com/testfile/upload": Invalid value for seconds_since_epoch
step returned non-zero exit code: 1

Example:

https://luci-milo.appspot.com/buildbot/chromium.android.fyi/Memory%20Infra%20Tester/11989 ; https://luci-logdog.appspot.com/v/?s=chromium%2Fbb%2Fchromium.android.fyi%2FMemory_Infra_Tester%2F11989%2F%2B%2Frecipes%2Fsteps%2FUpload_to_test-results__system_health.memory_mobile_%2F0%2Fstdout