Only deactivate SupervisedUserService when removing its delegate.

chrome/browser/supervised_user/supervised_user_service.cc

 // Copyright 2014 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/supervised_user/supervised_user_service.h"
 
 #include "base/command_line.h"
 #include "base/memory/ref_counted.h"
 #include "base/prefs/pref_service.h"
 #include "base/strings/string_number_conversions.h"
@@ skipping 180 matching lines @@
       prefs::kSupervisedUserSecondCustodianName, std::string(),
       user_prefs::PrefRegistrySyncable::UNSYNCABLE_PREF);
   registry->RegisterStringPref(
       prefs::kSupervisedUserSecondCustodianProfileImageURL, std::string(),
       user_prefs::PrefRegistrySyncable::UNSYNCABLE_PREF);
   registry->RegisterBooleanPref(prefs::kSupervisedUserCreationAllowed, true,
       user_prefs::PrefRegistrySyncable::UNSYNCABLE_PREF);
 }
 
 void SupervisedUserService::SetDelegate(Delegate* delegate) {
-  if (delegate_ == delegate)
-    return;
-  // If the delegate changed, deactivate first to give the old delegate a chance
-  // to clean up.
-  SetActive(false);
+  if (delegate) {
+    // Changing delegates isn't allowed.
+    DCHECK(!delegate_);
+  } else {
+    // If the delegate is removed, deactivate first to give the old delegate a
+    // chance to clean up.
+    SetActive(false);
+  }
   delegate_ = delegate;
 }
 
 scoped_refptr<const SupervisedUserURLFilter>
 SupervisedUserService::GetURLFilterForIOThread() {
   return url_filter_context_.io_url_filter();
 }
 
 SupervisedUserURLFilter* SupervisedUserService::GetURLFilterForUIThread() {
   return url_filter_context_.ui_url_filter();
@@ skipping 566 matching lines @@
   // The active user can be NULL in unit tests.
   if (chromeos::UserManager::Get()->GetActiveUser()) {
     return UTF16ToUTF8(chromeos::UserManager::Get()->GetUserDisplayName(
         chromeos::UserManager::Get()->GetActiveUser()->GetUserID()));
   }
   return std::string();
 #else
   return profile_->GetPrefs()->GetString(prefs::kProfileName);
 #endif
 }