Fix typo in ct-failures

TBR=dgrogan@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/596263004

git-svn-id: svn://svn.chromium.org/blink/trunk@182638 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Add a runtime enabled feature for Background Sync.

Background Sync is feature that dispatches events to a Service Worker
but is separate from Service Workers. Ideally it would be its own
module like push_messaging, but for now just add its own runtime
enabled feature. This lets us unblock shipping Service Worker from
Background Sync.

BUG=415888

Review URL: https://codereview.chromium.org/586653002

git-svn-id: svn://svn.chromium.org/blink/trunk@182639 bbb929c8-8fbe-4397-9dbb-9b2b20218538