This has been causing WPT imports to fail for the past few days. From https://ci.chromium.org/buildbot/chromium.infra.cron/wpt-importer/8733, for example:

2017-12-27 01:44:12,290 - All jobs finished.
2017-12-27 01:44:12,291 - Adding test expectations lines to LayoutTests/TestExpectations.
2017-12-27 01:44:23,554 - Tests to rebaseline:
2017-12-27 01:44:23,555 -   external/wpt/websockets/opening-handshake/005.html?wss
2017-12-27 01:44:42,301 - Lines to write to TestExpectations:
2017-12-27 01:44:42,302 -   crbug.com/626703 external/wpt/websockets/keeping-connection-open/001.html?wss [ Timeout ]
2017-12-27 01:44:42,302 -   crbug.com/626703 external/wpt/websockets/constructor/014.html?wss [ Timeout ]
2017-12-27 01:44:43,269 - Generating MANIFEST.json
2017-12-27 01:44:48,940 - Committing changes.
Traceback (most recent call last):
  File "/mnt/data/b/rr/tmp9ekTxk/w/src/third_party/WebKit/Tools/Scripts/wpt-import", line 24, in <module>
    main()
  File "/mnt/data/b/rr/tmp9ekTxk/w/src/third_party/WebKit/Tools/Scripts/wpt-import", line 17, in main
    host.exit(importer.main())
  File "/mnt/data/b/rr/tmp9ekTxk/w/src/third_party/WebKit/Tools/Scripts/webkitpy/w3c/test_importer.py", line 162, in main
    if not self.update_expectations_for_cl():
  File "/mnt/data/b/rr/tmp9ekTxk/w/src/third_party/WebKit/Tools/Scripts/webkitpy/w3c/test_importer.py", line 208, in update_expectations_for_cl
    self._upload_patchset(message)
  File "/mnt/data/b/rr/tmp9ekTxk/w/src/third_party/WebKit/Tools/Scripts/webkitpy/w3c/test_importer.py", line 435, in _upload_patchset
    self.git_cl.run(['upload', '-f', '-t', message, '--gerrit'])
  File "/mnt/data/b/rr/tmp9ekTxk/w/src/third_party/WebKit/Tools/Scripts/webkitpy/common/net/git_cl.py", line 60, in run
    return self._host.executive.run_command(command, cwd=self._cwd)
  File "/mnt/data/b/rr/tmp9ekTxk/w/src/third_party/WebKit/Tools/Scripts/webkitpy/common/system/executive.py", line 337, in run_command
    (error_handler or self.default_error_handler)(script_error)
  File "/mnt/data/b/rr/tmp9ekTxk/w/src/third_party/WebKit/Tools/Scripts/webkitpy/common/system/executive.py", line 244, in default_error_handler
    raise error
webkitpy.common.system.executive.ScriptError: Failed to run "['git', 'cl', 'upload', '-f', '-t', 'Update test expectations and baselines.', '--gerrit']" exit_code: 1
output: Last 500 characters of output:
ml?wss
third_party/WebKit/LayoutTests/TestExpectations:2782 Duplicate or ambiguous entry lines third_party/WebKit/LayoutTests/TestExpectations:1931 and third_party/WebKit/LayoutTests/TestExpectations:2782. external/wpt/websockets/keeping-connection-open/001.html?wss
Lint failed.

external/wpt/websockets/keeping-connection-open/001.html?wss has an entry in TestExpectations that current looks like this:

    crbug.com/709227 external/wpt/websockets/keeping-connection-open/001.html?wss [ Failure ]

whereas wpt_expectations_updater.py is trying to add a new entry that looks like this:

    crbug.com/626703 external/wpt/websockets/keeping-connection-open/001.html?wss [ Timeout ]

instead of updating the existing TestExpecations entry.