Adding mojo calls for easy unlock service

BUG=721524

Review-Url: https://codereview.chromium.org/2903353003
Cr-Commit-Position: refs/heads/master@{#477722}

• ash/login/lock_screen_controller.cc[diff]
• ash/login/lock_screen_controller.h[diff]
• ash/login/lock_screen_controller_unittest.cc[diff]
• ash/login/mock_lock_screen_client.h[diff]
• ash/public/interfaces/lock_screen.mojom[diff]
• chrome/browser/chromeos/BUILD.gn[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[Added - diff]
• chrome/browser/chromeos/login/lock/views_screen_locker.h[Added - diff]
• chrome/browser/chromeos/login/screens/user_selection_screen.cc[diff]
• chrome/browser/chromeos/login/screens/user_selection_screen.h[diff]
• chrome/browser/chromeos/login/ui/views/user_board_view.h[diff]
• chrome/browser/chromeos/login/user_selection_screen_proxy.cc[Added - diff]
• chrome/browser/chromeos/login/user_selection_screen_proxy.h[Added - diff]
• chrome/browser/ui/ash/lock_screen_client.cc[diff]
• chrome/browser/ui/ash/lock_screen_client.h[diff]
• chrome/browser/ui/webui/chromeos/login/user_board_screen_handler.cc[diff]
• chrome/browser/ui/webui/chromeos/login/user_board_screen_handler.h[diff]
• components/proximity_auth/screenlock_bridge.cc[diff]
• components/proximity_auth/screenlock_bridge.h[diff]