Reland cros: Views login backend for removing users.

Relands https://chromium-review.googlesource.com/c/chromium/src/+/935675. It was
reverted in https://chromium-review.googlesource.com/c/chromium/src/+/969228

TBR: xiyuan@chromium.org
TBR: dcheng@chromium.org
Bug: 809637
Change-Id: I9e44d96cbe26bc090e177460e18542b8b4d387b2
Reviewed-on: https://chromium-review.googlesource.com/971161
Reviewed-by: Jacob Dufault <jdufault@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Jacob Dufault <jdufault@chromium.org>
Cr-Commit-Position: refs/heads/master@{#544423}

diff --git a/ash/login/login_screen_controller.cc b/ash/login/login_screen_controller.cc
index e024c81..1f4f88c 100644
--- a/ash/login/login_screen_controller.cc
+++ b/ash/login/login_screen_controller.cc

@@ -312,6 +312,18 @@
   login_screen_client_->ShowGaiaSignin();
 }
 
+void LoginScreenController::OnRemoveUserWarningShown() {
+  if (!login_screen_client_)
+    return;
+  login_screen_client_->OnRemoveUserWarningShown();
+}
+
+void LoginScreenController::RemoveUser(const AccountId& account_id) {
+  if (!login_screen_client_)
+    return;
+  login_screen_client_->RemoveUser(account_id);
+}
+
 void LoginScreenController::AddLockScreenAppsFocusObserver(
     LockScreenAppsFocusObserver* observer) {
   lock_screen_apps_focus_observers_.AddObserver(observer);