[Webauthn] Enable the Web Authentication API by default on desktop platforms.
TBR=darin@chromium.org

Intent to ship thread:
https://groups.google.com/a/chromium.org/forum/#!searchin/blink-dev/intent$20ship$20web$20authentication$20api$20/blink-dev/o9RU6Vv0xeM/EGnQOExbAAAJ

Bug: 664630
Change-Id: I617cec25080b4ec9df929b81494c82e04212047d
Reviewed-on: https://chromium-review.googlesource.com/977031
Commit-Queue: Kim Paulhamus <kpaulhamus@chromium.org>
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Reviewed-by: Antoine Labour <piman@chromium.org>
Reviewed-by: Balazs Engedy <engedy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#547371}
8 files changed