device/fido: add PIN support to makeCredential and getAssertion.

This change adds additional PIN logic to these flows, although the UI
isn't fully hooked up yet. This is guarded by a feature flag and the
intent is that there's no behaviour change without the feature flag
being set.

BUG=870892

Change-Id: Idd718c5b1ed76e1acd3d4041339b63f910fff41a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1493433
Commit-Queue: Martin Kreichgauer <martinkr@google.com>
Reviewed-by: Martin Kreichgauer <martinkr@google.com>
Reviewed-by: Avi Drissman <avi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#637502}
30 files changed