Remove PrefValueStore's dependency on PrefModelAssociator.

chrome/browser/prefs/pref_service_syncable.cc

Index: chrome/browser/prefs/pref_service_syncable.cc
diff --git a/chrome/browser/prefs/pref_service_syncable.cc b/chrome/browser/prefs/pref_service_syncable.cc
index 7cf7874d4d26deab5cc0c68b2d77da89ec71efe2..46a35176540a910239a6278a956b6a9e0f60dc47 100644
--- a/chrome/browser/prefs/pref_service_syncable.cc
+++ b/chrome/browser/prefs/pref_service_syncable.cc
@@ -78,7 +78,10 @@ PrefServiceSyncable::PrefServiceSyncable(
                 read_error_callback,
                 async) {
   pref_sync_associator_.SetPrefService(this);
-  pref_value_store->set_sync_associator(&pref_sync_associator_);
+
+  pref_value_store->set_callback(
+      base::Bind(&PrefModelAssociator::ProcessPrefChange,
+                 base::Unretained(&pref_sync_associator_)));
 }
 
 PrefServiceSyncable::~PrefServiceSyncable() {}