Populate password into mojo api.

ash/login/ui/login_auth_user_view.cc

Index: ash/login/ui/login_auth_user_view.cc
diff --git a/ash/login/ui/login_auth_user_view.cc b/ash/login/ui/login_auth_user_view.cc
index b9fa5baea867c6c3e9ca838da17bcbf0fe45bf32..9300411c996371267abfbadb485237ee109221ce 100644
--- a/ash/login/ui/login_auth_user_view.cc
+++ b/ash/login/ui/login_auth_user_view.cc
@@ -11,6 +11,7 @@
 #include "ash/login/ui/login_pin_view.h"
 #include "ash/login/ui/login_user_view.h"
 #include "ash/shell.h"
+#include "base/strings/utf_string_conversions.h"
 #include "components/user_manager/user.h"
 #include "ui/views/layout/box_layout.h"
 #include "ui/views/view.h"
@@ -120,7 +121,7 @@ gfx::Size LoginAuthUserView::CalculatePreferredSize() const {
 void LoginAuthUserView::OnAuthSubmit(bool is_pin,
                                      const base::string16& password) {
   Shell::Get()->lock_screen_controller()->AuthenticateUser(
-      current_user_, std::string(), is_pin,
+      current_user_, UTF16ToUTF8(password), is_pin,
       base::BindOnce([](OnAuthCallback on_auth,
                         bool auth_success) { on_auth.Run(auth_success); },
                      on_auth_));