[WebAuthn] Move support for BLE authenticators behind a content switch

Bug: 664630
Change-Id: I33752d771686b3c935b12bf13d1962cf456a32cd
Reviewed-on: https://chromium-review.googlesource.com/978506
Commit-Queue: Kim Paulhamus <kpaulhamus@chromium.org>
Reviewed-by: Antoine Labour <piman@chromium.org>
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Balazs Engedy <engedy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#546662}
5 files changed