Add U2fTransportProtocol.kNearFieldCommunication.

This results in device::U2fTransportProtocol now having the exact same
enumerators as webauth::mojom::AuthenticatorTransport, so a type mapping
is also added between the two enums.

Furthermore, as we do not yet support NFC discovery (the work has not
started yet, tracked by crbug.com/825949), the semantics of
FidoDiscovery::Create has been changed so that it is now allowed to
return nullptr for transports not supported on a platform.

[email protected]

Bug: 785955
Change-Id: Ia142504e0fd73200a96b4292be83debf1f1aa553
Reviewed-on: https://chromium-review.googlesource.com/980889
Reviewed-by: John Abd-El-Malek <[email protected]>
Reviewed-by: Balazs Engedy <[email protected]>
Reviewed-by: Mike West <[email protected]>
Reviewed-by: Daniel Cheng <[email protected]>
Reviewed-by: Kim Paulhamus <[email protected]>
Commit-Queue: Balazs Engedy <[email protected]>
Cr-Commit-Position: refs/heads/master@{#547139}
9 files changed