https://ci.chromium.org/p/chromium/builders/luci.chromium.try/linux-blink-gen-property-trees/629:

Command: /b/s/w/ir/.swarming_module_cache/vpython/dba151/bin/python ../../third_party/blink/tools/run_web_tests.py --seed 4 --no-show-results --zero-tests-executed-ok --clobber-old-results --exit-after-n-failures 5000 --exit-after-n-crashes-or-timeouts 100 --debug-rwt-logging --results-directory /b/s/w/ioqzhQP7/layout-test-results --num-retries=3 --debug --additional-driver-flag=--enable-blink-gen-property-trees --write-full-results-to /b/s/w/ioqzhQP7/output.json

13:47:39.217 10713 Driver cannot be found in common build directories.
+-----------------------------------------------------------------------------------+
| End of shard 0                                                                    |
|  Pending: 0.5s  Duration: 1.1s  Bot: gce-trusty-e833d7b0-us-west1-c-nw79  Exit: 0 |
+-----------------------------------------------------------------------------------+
Total duration: 1.1s
WARNING:root:No shard json files found in task_output_dir: '/b/swarming/w/ir/tmp/t/tmpDKAI62'
Found ['/b/swarming/w/ir/tmp/t/tmpDKAI62/summary.json']
Running ['/b/swarming/w/ir/cache/vpython/045a04/bin/python', '/b/swarming/w/ir/cache/builder/src/third_party/blink/tools/merge_web_test_results.py', '--build-properties', '{"blamelist": ["wangxianzhu@chromium.org"], "bot_id": "swarm1100-c4", "buildbucket": {"build": {"bucket": "luci.chromium.try", "created_by": "user:wangxianzhu@google.com", "created_ts": 1540153954599072, "id": "8932025242860441616", "project": "chromium", "tags": ["buildset:patch/gerrit/chromium-review.googlesource.com/1293173/2", "user_agent:gerrit"]}, "hostname": "cr-buildbucket.appspot.com"}, "buildername": "linux-blink-gen-property-trees", "buildnumber": 629, "got_angle_revision": "0cc11c684b5465b73ff107f7935ae72ca1dbbcff", "got_buildtools_revision": "13a00f110ef910a25763346d6538b60f12845656", "got_nacl_revision": "99673869a3cd8731d924bd32fa486feebfdc6c4f", "got_revision": "a93d048f9be00cdd061bdf6db4f512dd4beee34d", "got_revision_cp": "refs/heads/master@{#601457}", "got_swarming_client_revision": "f78187ab77127de42555afe0ad410bebde6ac6a5", "got_v8_revision": "d206a4b910f4138c15e04cf77544175ef7ffbe26", "got_v8_revision_cp": "refs/heads/7.2.45@{#1}", "got_webrtc_revision": "648d28ad62573c7b1a1e5b05a6122227f7272950", "got_webrtc_revision_cp": "refs/heads/master@{#25280}", "mastername": "tryserver.chromium.linux", "patch_gerrit_url": "https://chromium-review.googlesource.com", "patch_issue": 1293173, "patch_project": "chromium/src", "patch_ref": "refs/changes/73/1293173/2", "patch_repository_url": "https://chromium.googlesource.com/chromium/src", "patch_set": 2, "patch_storage": "gerrit", "path_config": "generic", "recipe": "chromium_trybot", "repository": "https://chromium.googlesource.com/chromium/src"}', '--summary-json', '/b/swarming/w/ir/tmp/t/tmpDKAI62/summary.json', '--task-output-dir', '/b/swarming/w/ir/tmp/t/tmpDKAI62', u'--verbose', '-o', '/b/swarming/w/ir/tmp/t/tmpLGq0ZD.json'] in None (env: None)
2018-10-21 13:47:47,824 - blinkpy.common.system.log_utils: [DEBUG] Debug logging enabled.
2018-10-21 13:47:47,825 - root: [INFO] Running with isolated arguments
Traceback (most recent call last):
  File "/b/swarming/w/ir/cache/builder/src/third_party/blink/tools/merge_web_test_results.py", line 12, in <module>
    main(sys.argv[1:])
  File "/b/swarming/w/ir/cache/builder/src/third_party/blink/tools/blinkpy/web_tests/merge_results.py", line 776, in main
    assert args.positional
AssertionError
Command ['/b/swarming/w/ir/cache/vpython/045a04/bin/python', '/b/swarming/w/ir/cache/builder/src/third_party/blink/tools/merge_web_test_results.py', '--build-properties', '{"blamelist": ["wangxianzhu@chromium.org"], "bot_id": "swarm1100-c4", "buildbucket": {"build": {"bucket": "luci.chromium.try", "created_by": "user:wangxianzhu@google.com", "created_ts": 1540153954599072, "id": "8932025242860441616", "project": "chromium", "tags": ["buildset:patch/gerrit/chromium-review.googlesource.com/1293173/2", "user_agent:gerrit"]}, "hostname": "cr-buildbucket.appspot.com"}, "buildername": "linux-blink-gen-property-trees", "buildnumber": 629, "got_angle_revision": "0cc11c684b5465b73ff107f7935ae72ca1dbbcff", "got_buildtools_revision": "13a00f110ef910a25763346d6538b60f12845656", "got_nacl_revision": "99673869a3cd8731d924bd32fa486feebfdc6c4f", "got_revision": "a93d048f9be00cdd061bdf6db4f512dd4beee34d", "got_revision_cp": "refs/heads/master@{#601457}", "got_swarming_client_revision": "f78187ab77127de42555afe0ad410bebde6ac6a5", "got_v8_revision": "d206a4b910f4138c15e04cf77544175ef7ffbe26", "got_v8_revision_cp": "refs/heads/7.2.45@{#1}", "got_webrtc_revision": "648d28ad62573c7b1a1e5b05a6122227f7272950", "got_webrtc_revision_cp": "refs/heads/master@{#25280}", "mastername": "tryserver.chromium.linux", "patch_gerrit_url": "https://chromium-review.googlesource.com", "patch_issue": 1293173, "patch_project": "chromium/src", "patch_ref": "refs/changes/73/1293173/2", "patch_repository_url": "https://chromium.googlesource.com/chromium/src", "patch_set": 2, "patch_storage": "gerrit", "path_config": "generic", "recipe": "chromium_trybot", "repository": "https://chromium.googlesource.com/chromium/src"}', '--summary-json', '/b/swarming/w/ir/tmp/t/tmpDKAI62/summary.json', '--task-output-dir', '/b/swarming/w/ir/tmp/t/tmpDKAI62', u'--verbose', '-o', '/b/swarming/w/ir/tmp/t/tmpLGq0ZD.json'] returned exit code 1
WARNING:root:merge_cmd had non-zero return code: 1
step returned non-zero exit code: 1