webauthn: add special error sheet for GetAssertion on internal transport

This adds a special error screen for GetAssertion requests that are
about to be dispatched to Touch ID but there is no available credential
in the keychain. The screen can be reached by selecting Touch ID from
the transport selection UI. If Touch ID is the only available transport,
the UI auto advances to the error screen.

This also fixes a bug where the UI auto advanced to the regular Touch ID
screen on GetAssertion even though no matching credential was present.

Bug: 678128,847985
Change-Id: Ia4ce02a495821c7d0a3caa34c7a2e7eaeb1cbc42
Reviewed-on: https://chromium-review.googlesource.com/1194954
Commit-Queue: Martin Kreichgauer <martinkr@google.com>
Reviewed-by: Balazs Engedy <engedy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#587140}
6 files changed