[Sync] Make ModelSafeWorker a true interface

chrome/browser/sync/glue/browser_thread_model_worker.h

Index: chrome/browser/sync/glue/browser_thread_model_worker.h
diff --git a/chrome/browser/sync/glue/browser_thread_model_worker.h b/chrome/browser/sync/glue/browser_thread_model_worker.h
index 843b9dad456d062f891ad94deeb58e8dee3d9b61..6fde3eaec27a3b260992aa9fc3d541b962acb0ad 100644
--- a/chrome/browser/sync/glue/browser_thread_model_worker.h
+++ b/chrome/browser/sync/glue/browser_thread_model_worker.h
@@ -22,7 +22,7 @@ namespace browser_sync {
 // A ModelSafeWorker for models that accept requests from the syncapi that need
 // to be fulfilled on a browser thread, for example autofill on the DB thread.
 // TODO(sync): Try to generalize other ModelWorkers (e.g. history, etc).
-class BrowserThreadModelWorker : public browser_sync::ModelSafeWorker {
+class BrowserThreadModelWorker : public ModelSafeWorker {
  public:
   BrowserThreadModelWorker(content::BrowserThread::ID thread,
                            ModelSafeGroup group);