[Sync] Make ModelSafeWorker a true interface

chrome/browser/sync/engine/model_safe_worker.cc

Index: chrome/browser/sync/engine/model_safe_worker.cc
diff --git a/chrome/browser/sync/engine/model_safe_worker.cc b/chrome/browser/sync/engine/model_safe_worker.cc
index 907d75efd083679a95c29fa1461e5e540e97da48..4ac96fb70f77e4b88dfef51663ce0854f0ffa2c2 100644
--- a/chrome/browser/sync/engine/model_safe_worker.cc
+++ b/chrome/browser/sync/engine/model_safe_worker.cc
@@ -71,18 +71,6 @@ std::string ModelSafeGroupToString(ModelSafeGroup group) {
   }
 }
 
-ModelSafeWorker::ModelSafeWorker() {}
-
 ModelSafeWorker::~ModelSafeWorker() {}
 
-UnrecoverableErrorInfo ModelSafeWorker::DoWorkAndWaitUntilDone(
-  const WorkCallback& work) {
-  // For GROUP_PASSIVE, we do the work on the current thread.
-  return work.Run();
-}
-
-ModelSafeGroup ModelSafeWorker::GetModelSafeGroup() {
-  return GROUP_PASSIVE;
-}
-
 }  // namespace browser_sync