Fix checkbox alignment.

Fixed checkboxes: "Async", "Preserve log", "Capture stacks".

Tested on Linux and Mac.

NOTRY=true
BUG=

Review URL: https://codereview.chromium.org/137383013

git-svn-id: svn://svn.chromium.org/blink/trunk@166462 bbb929c8-8fbe-4397-9dbb-9b2b20218538