Make EnrollmentScreen::SetParameters() idempotent.

chrome/browser/chromeos/login/enrollment/enrollment_screen.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/chromeos/login/enrollment/enrollment_screen.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/logging.h"
 #include "base/message_loop/message_loop.h"
@@ skipping 55 matching lines @@
     EnrollmentScreenActor::EnrollmentMode enrollment_mode,
     const std::string& management_domain,
     const std::string& user,
     const std::string& auth_token,
     pairing_chromeos::ControllerPairingController* shark_controller,
     pairing_chromeos::HostPairingController* remora_controller) {
   enrollment_mode_ = enrollment_mode;
   user_ = user.empty() ? user : gaia::CanonicalizeEmail(user);
   auth_token_ = auth_token;
   shark_controller_ = shark_controller;
-  DCHECK(!remora_controller_);
+  if (remora_controller_)
+    remora_controller_->RemoveObserver(this);
   remora_controller_ = remora_controller;
   if (remora_controller_)
     remora_controller_->AddObserver(this);
   actor_->SetParameters(this, enrollment_mode_, management_domain);
 }
 
 void EnrollmentScreen::PrepareToShow() {
   actor_->PrepareToShow();
 }
 
@@ skipping 305 matching lines @@
     sample = policy::kMetricEnrollmentAutoFailed;
   UMA(sample);
 }
 
 void EnrollmentScreen::ShowSigninScreen() {
   actor_->Show();
   actor_->ShowSigninScreen();
 }
 
 }  // namespace chromeos