Split PrefService into PrefService, PrefServiceSimple and PrefServiceSyncable.

chrome/browser/prefs/pref_model_associator.h

Index: chrome/browser/prefs/pref_model_associator.h
diff --git a/chrome/browser/prefs/pref_model_associator.h b/chrome/browser/prefs/pref_model_associator.h
index 7229f11fdd3f761a38423fe5dfd377a81b2402d2..d5bceca28e25768fd2e2d93aa158a157dfff9af4 100644
--- a/chrome/browser/prefs/pref_model_associator.h
+++ b/chrome/browser/prefs/pref_model_associator.h
@@ -12,10 +12,11 @@
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/threading/non_thread_safe.h"
-#include "chrome/browser/prefs/pref_service.h"
 #include "sync/api/sync_data.h"
 #include "sync/api/syncable_service.h"
 
+class PrefService;
+
 namespace sync_pb {
 class PreferenceSpecifics;
 }