cros: Add a ShowResetScreen method for showing the powerwash dialog.

This will be used by LockContentsView in a future CL to implement the
powerwash shortcut in views-login.

TBR=dcheng@chromium.org

Bug: 837501
Change-Id: If1b120ed7a3bfb741adfda3ed99c8a4bb33dd026
Reviewed-on: https://chromium-review.googlesource.com/1143885
Commit-Queue: Quan Nguyen <qnnguyen@chromium.org>
Reviewed-by: Jacob Dufault <jdufault@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576677}

diff --git a/ash/login/login_screen_controller.cc b/ash/login/login_screen_controller.cc
index eb5d40d..e90acfe1b 100644
--- a/ash/login/login_screen_controller.cc
+++ b/ash/login/login_screen_controller.cc

@@ -429,6 +429,10 @@
   login_screen_client_->LaunchArcKioskApp(account_id);
 }
 
+void LoginScreenController::ShowResetScreen() {
+  login_screen_client_->ShowResetScreen();
+}
+
 void LoginScreenController::DoAuthenticateUser(const AccountId& account_id,
                                                const std::string& password,
                                                bool authenticated_by_pin,