Refactor preference syncing.

chrome/browser/sync/profile_sync_service.h

Index: chrome/browser/sync/profile_sync_service.h
diff --git a/chrome/browser/sync/profile_sync_service.h b/chrome/browser/sync/profile_sync_service.h
index ecafd6993622c8c1223a4659ff47cb56425eae2a..3bd52dce7b4ea030bba0db61672a324fdf6ac83d 100644
--- a/chrome/browser/sync/profile_sync_service.h
+++ b/chrome/browser/sync/profile_sync_service.h
@@ -45,6 +45,7 @@ class BackendMigrator;
 class ChangeProcessor;
 class DataTypeManager;
 class JsFrontend;
+class NewAssociatorInterface;
 class SessionModelAssociator;
 namespace sessions { struct SyncSessionSnapshot; }
 }
@@ -381,6 +382,13 @@ class ProfileSyncService : public browser_sync::SyncFrontend,
       syncable::AutofillMigrationDebugInfo::PropertyToSet property_to_set,
       const syncable::AutofillMigrationDebugInfo& info);
 
+  // Register a model associator with the profile sync service. This will
+  // link the associator to the datatype controller corresponding to
+  // associator's type. If the datatype controller does not exist, the request
+  // is dropped silently.
+  virtual void RegisterModelAssociator(
+      browser_sync::NewAssociatorInterface* associator);
+
   virtual void ActivateDataType(
       browser_sync::DataTypeController* data_type_controller,
       browser_sync::ChangeProcessor* change_processor);