UI stub for smart card unlock on Lock Screen

1. Wire up the Chrome OS Lock Screen UI code with the
   challenge-response authentication (a.k.a. smart card login)
   bits from the browser process.

2. Add a UI control into the Lock Screen for starting the
   challenge-response authentication. (The UI control is
   temporarily an unstyled button, but will be replaced with the
   real UI in follow-ups.)

Bug: 964069
Test: enroll a Chromebook, configure device policies to force-install smart card middleware onto Login Screen, log in using a SAML account that uses smart card authentication, lock the Chromebook, check that "Unlock with smart card" appears, click it, check that the user session gets unlocked
Change-Id: Icf0ccc80b6778d318c115f79072fdd6595a034b1
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1720640
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Roman Sorokin [CET] <rsorokin@chromium.org>
Commit-Queue: Maksim Ivanov <emaxx@chromium.org>
Cr-Commit-Position: refs/heads/master@{#681896}

• ash/login/login_screen_controller.cc[diff]
• ash/login/login_screen_controller.h[diff]
• ash/login/mock_login_screen_client.cc[diff]
• ash/login/mock_login_screen_client.h[diff]
• ash/login/ui/lock_contents_view.cc[diff]
• ash/login/ui/lock_contents_view.h[diff]
• ash/login/ui/login_auth_user_view.cc[diff]
• ash/login/ui/login_auth_user_view.h[diff]
• ash/login/ui/login_data_dispatcher.cc[diff]
• ash/login/ui/login_data_dispatcher.h[diff]
• ash/public/cpp/login_screen_client.h[diff]
• ash/public/cpp/login_screen_model.h[diff]
• chrome/browser/chromeos/login/lock/screen_locker.cc[diff]
• chrome/browser/chromeos/login/lock/screen_locker.h[diff]
• chrome/browser/chromeos/login/lock/views_screen_locker.cc[diff]
• chrome/browser/chromeos/login/lock/views_screen_locker.h[diff]
• chrome/browser/chromeos/login/login_auth_recorder.cc[diff]
• chrome/browser/chromeos/login/login_auth_recorder.h[diff]
• chrome/browser/chromeos/login/ui/login_display_host_mojo.cc[diff]
• chrome/browser/chromeos/login/ui/login_display_host_mojo.h[diff]
• chrome/browser/ui/ash/login_screen_client.cc[diff]
• chrome/browser/ui/ash/login_screen_client.h[diff]
• chrome/browser/ui/ash/test_login_screen_model.cc[diff]
• chrome/browser/ui/ash/test_login_screen_model.h[diff]
• tools/metrics/histograms/enums.xml[diff]