Starting at https://ci.chromium.org/p/infra/builders/luci.infra.cron/wpt-importer/b8928846416598875072 (2018-11-25 22:38 UTC) import has been failing in this manner:

2018-11-25 14:40:34,269 - WPT checkout exists at /tmp/wpt, fetching latest
2018-11-25 14:40:35,753 - Importing wpt@e94ae4b34ee6fa3b7d608a011818f34757193725 to Chromium 77578ccb4082ae20a9326d9e673225f1189ebb63
Traceback (most recent call last):
  File "/b/swarming/w/ir/kitchen-workdir/src/third_party/blink/tools/wpt_import.py", line 26, in <module>
    main()
  File "/b/swarming/w/ir/kitchen-workdir/src/third_party/blink/tools/wpt_import.py", line 19, in main
    host.exit(importer.main())
  File "/b/swarming/w/ir/kitchen-workdir/src/third_party/blink/tools/blinkpy/w3c/test_importer.py", line 131, in main
    commits = self.apply_exportable_commits_locally(local_wpt)
  File "/b/swarming/w/ir/kitchen-workdir/src/third_party/blink/tools/blinkpy/w3c/test_importer.py", line 337, in apply_exportable_commits_locally
    commits = self.exportable_but_not_exported_commits(local_wpt)
  File "/b/swarming/w/ir/kitchen-workdir/src/third_party/blink/tools/blinkpy/w3c/test_importer.py", line 368, in exportable_but_not_exported_commits
    self.host, local_wpt, self.wpt_github, require_clean=False, verify_merged_pr=True)
  File "/b/swarming/w/ir/kitchen-workdir/src/third_party/blink/tools/blinkpy/w3c/chromium_exportable_commits.py", line 47, in exportable_commits_over_last_n_commits
    return _exportable_commits_since(start_commit, host, local_wpt, wpt_github, require_clean, verify_merged_pr)
  File "/b/swarming/w/ir/kitchen-workdir/src/third_party/blink/tools/blinkpy/w3c/chromium_exportable_commits.py", line 73, in _exportable_commits_since
    state, error = get_commit_export_state(commit, local_wpt, wpt_github, verify_merged_pr)
  File "/b/swarming/w/ir/kitchen-workdir/src/third_party/blink/tools/blinkpy/w3c/chromium_exportable_commits.py", line 106, in get_commit_export_state
    patch = chromium_commit.format_patch()
  File "/b/swarming/w/ir/kitchen-workdir/src/third_party/blink/tools/blinkpy/w3c/chromium_commit.py", line 121, in format_patch
    ] + filtered_files, cwd=self.absolute_chromium_dir)
  File "/b/swarming/w/ir/kitchen-workdir/src/third_party/blink/tools/blinkpy/common/system/executive.py", line 319, in run_command
    close_fds=self._should_close_fds())
  File "/b/swarming/w/ir/kitchen-workdir/src/third_party/blink/tools/blinkpy/common/system/executive.py", line 393, in popen
    return subprocess.Popen(string_args, **kwargs)
  File "/b/swarming/w/ir/cipd_bin_packages/lib/python2.7/subprocess.py", line 390, in __init__
    errread, errwrite)
  File "/b/swarming/w/ir/cipd_bin_packages/lib/python2.7/subprocess.py", line 1025, in _execute_child
    raise child_exception
OSError: [Errno 7] Argument list too long
step returned non-zero exit code: 1