sync: don't allow NULL profile in ProfileSyncService and friends

chrome/browser/sync/sync_prefs.h

Index: chrome/browser/sync/sync_prefs.h
diff --git a/chrome/browser/sync/sync_prefs.h b/chrome/browser/sync/sync_prefs.h
index 5a1f1f027141f3540f25252e4347155a676c38db..b46c001a9f1240375dbaae9952145ae67ece8ec6 100644
--- a/chrome/browser/sync/sync_prefs.h
+++ b/chrome/browser/sync/sync_prefs.h
@@ -50,9 +50,8 @@ class SyncPrefObserver {
 class SyncPrefs : NON_EXPORTED_BASE(public base::NonThreadSafe),
                   public base::SupportsWeakPtr<SyncPrefs> {
  public:
-  // |pref_service| may be NULL (for unit tests), but in that case no
-  // setter methods should be called.  Does not take ownership of
-  // |pref_service|.
+  // |pref_service| may not be NULL.
+  // Does not take ownership of |pref_service|.
   explicit SyncPrefs(PrefService* pref_service);
 
   virtual ~SyncPrefs();