[webauthn] Add {add|remove}VirtualAuthenticator to Devtools Domain

Add addVirtualAuthenticator and removeVirtualAuthenticator to the
WebAuthn Devtools Domain. Patch VirtualFidoDevice so that it no longer
hardcodes the transport declared on attestation, this makes testing
different authenticators easier.

This is one in a series of patches intended to create a Testing API for
WebAuthn, for use in Web Platform Tests and by external webauthn tests.

For an overview of overall design, please see
https://docs.google.com/document/d/1bp2cMgjm2HSpvL9-WsJoIQMsBi1oKGQY6CvWD-9WmIQ/edit?usp=sharing

Bug: 922572
Change-Id: Ib606a265576b8059d3a347c63b26a30574136538
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1636828
Commit-Queue: Nina Satragno <nsatragno@chromium.org>
Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Reviewed-by: Ken Buchanan <kenrb@chromium.org>
Reviewed-by: Kim Paulhamus <kpaulhamus@chromium.org>
Cr-Commit-Position: refs/heads/master@{#666101}
21 files changed