webkit_python_tests failing on 2 builders

Builders failed on: 
- WebKit Linux Trusty: 
  https://build.chromium.org/p/chromium.webkit/builders/WebKit%20Linux%20Trusty
- WebKit Linux Trusty Leak: 
  https://build.chromium.org/p/chromium.webkit/builders/WebKit%20Linux%20Trusty%20Leak

It's the git unitests that are failing with exit code 128.

Which appears to be some kind of permission denied or git lock file being present issue: http://stackoverflow.com/questions/9617336/how-to-resolve-git-did-not-exit-cleanly-exit-code-128-error-on-tortoisegit

I don't see anything in commit range that could have messed up git. Maybe some operation left a git lock file behind?