[Sync] Refactor non-frontend DTC to handle new API properly.

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 5e2189cfc375486907207b86f9cb3d8ccb15b722..e23edc9453921b74bfb13157ba0687c55ff1da86 100644
--- a/chrome/browser/prefs/pref_model_associator.h
+++ b/chrome/browser/prefs/pref_model_associator.h
@@ -12,6 +12,7 @@
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
+#include "base/memory/weak_ptr.h"
 #include "base/threading/non_thread_safe.h"
 #include "chrome/browser/prefs/pref_service.h"
 #include "chrome/browser/sync/api/syncable_service.h"
@@ -30,6 +31,7 @@ class Value;
 // PrefService from the local state PrefService.
 class PrefModelAssociator
     : public SyncableService,
+      public base::SupportsWeakPtr<PrefModelAssociator>,
       public base::NonThreadSafe {
  public:
   explicit PrefModelAssociator(PrefService* pref_service);