Rename one last WebKit -> blink namespace

My Python scripts missed this mention because it's in a script.

R=eseidel@chromium.org
BUG=295096

Review URL: https://codereview.chromium.org/62203005

git-svn-id: svn://svn.chromium.org/blink/trunk@161505 bbb929c8-8fbe-4397-9dbb-9b2b20218538