After updating to fc4297bd21581ad0af3980ea79c9ff4f0fdfb064 refs/heads/master@{#403800} I ran into the following error when trying to run webkit tests:

./third_party/WebKit/Tools/Scripts/run-webkit-tests
Traceback (most recent call last):
  File "./third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/run_webkit_tests.py", line 37, in <module>
    from webkitpy.common.host import Host
  File "./third_party/WebKit/Tools/Scripts/webkitpy/common/host.py", line 36, in <module>
    from webkitpy.common.net.buildbot import BuildBot
  File "./third_party/WebKit/Tools/Scripts/webkitpy/common/net/buildbot/__init__.py", line 5, in <module>
    
  File "./third_party/WebKit/Tools/Scripts/webkitpy/common/net/buildbot/buildbot.py", line 220, in <module>
  File "./third_party/WebKit/Tools/Scripts/webkitpy/common/net/buildbot/buildbot.py", line 222, in BuildBot
AttributeError: 'module' object has no attribute 'chromium_buildbot_url'

Removing the folder third_party/WebKit/Tools/Scripts/webkitpy/common/net/buildbot/ fixed the issue.