Python style cleanups after https://src.chromium.org/viewvc/blink?view=rev&revision=162322

R=eseidel@chromium.org
BUG=320036

Review URL: https://codereview.chromium.org/77733006

git-svn-id: svn://svn.chromium.org/blink/trunk@162405 bbb929c8-8fbe-4397-9dbb-9b2b20218538