SupervisedUserSyncService cleanup: Implement SigninManagerBase::Observer

chrome/browser/supervised_user/legacy/supervised_user_sync_service_factory.cc

Index: chrome/browser/supervised_user/legacy/supervised_user_sync_service_factory.cc
diff --git a/chrome/browser/supervised_user/legacy/supervised_user_sync_service_factory.cc b/chrome/browser/supervised_user/legacy/supervised_user_sync_service_factory.cc
index 973722c4674bf4c4c1211788d47b84358240af39..22d025cf69023e31406cc4cbd9e7757e934d76f7 100644
--- a/chrome/browser/supervised_user/legacy/supervised_user_sync_service_factory.cc
+++ b/chrome/browser/supervised_user/legacy/supervised_user_sync_service_factory.cc
@@ -5,6 +5,7 @@
 #include "chrome/browser/supervised_user/legacy/supervised_user_sync_service_factory.h"
 
 #include "chrome/browser/profiles/profile.h"
+#include "chrome/browser/signin/signin_manager_factory.h"
 #include "chrome/browser/supervised_user/legacy/supervised_user_sync_service.h"
 #include "components/keyed_service/content/browser_context_dependency_manager.h"
 
@@ -25,6 +26,7 @@ SupervisedUserSyncServiceFactory::SupervisedUserSyncServiceFactory()
     : BrowserContextKeyedServiceFactory(
           "SupervisedUserSyncService",
           BrowserContextDependencyManager::GetInstance()) {
+  DependsOn(SigninManagerFactory::GetInstance());
 }
 
 SupervisedUserSyncServiceFactory::~SupervisedUserSyncServiceFactory() {}
@@ -32,5 +34,5 @@ SupervisedUserSyncServiceFactory::~SupervisedUserSyncServiceFactory() {}
 KeyedService* SupervisedUserSyncServiceFactory::BuildServiceInstanceFor(
     content::BrowserContext* profile) const {
   return new SupervisedUserSyncService(
-      static_cast<Profile*>(profile)->GetPrefs());
+      static_cast<Profile*>(profile));
 }