remove c++11 enum scope in ServiceWorkerRegistration::OnRestoreFinished

Followup to CL 506043002: remove unneeded c++11 enum scope for
consistency (and since we haven't officially switched to c++11 yet).

BUG=398355

Review URL: https://codereview.chromium.org/560993002

Cr-Commit-Position: refs/heads/master@{#294311}
1 file changed