sync: Implement disabling of non blocking types

sync/internal_api/test/null_sync_core_proxy.cc

Index: sync/internal_api/test/null_sync_core_proxy.cc
diff --git a/sync/internal_api/test/null_sync_core_proxy.cc b/sync/internal_api/test/null_sync_core_proxy.cc
index 10fc7578af4c6528c12624d8fc8ace413685f9f9..e0c93f655431180fef7602bec22d284c8cca6f79 100644
--- a/sync/internal_api/test/null_sync_core_proxy.cc
+++ b/sync/internal_api/test/null_sync_core_proxy.cc
@@ -16,6 +16,10 @@ void NullSyncCoreProxy::ConnectTypeToCore(
   NOTREACHED() << "NullSyncCoreProxy is not meant to be used";
 }
 
+void NullSyncCoreProxy::Disconnect(syncer::ModelType type) {
+  NOTREACHED() << "NullSyncCoreProxy is not meant to be used";
+}
+
 scoped_ptr<SyncCoreProxy> NullSyncCoreProxy::Clone() const {
   return scoped_ptr<SyncCoreProxy>(new NullSyncCoreProxy());
 }