[Offline Pages] Adds new policy bits and reverse lookup.

This is part of the query API project to support looking up offline
pages by feature (which may contain multiple policies).  Also removes
the namespace check found in OfflinePageUtils.

BUG=622763

Review-Url: https://codereview.chromium.org/2364253002
Cr-Commit-Position: refs/heads/master@{#423912}
5 files changed