[Sync] Refactor ModelSafeWorker::DoWorkAndWaitUntilDone() to avoid code duplication.

components/sync/engine/passive_model_worker.h

Index: components/sync/engine/passive_model_worker.h
diff --git a/components/sync/engine/passive_model_worker.h b/components/sync/engine/passive_model_worker.h
index ac744dea9dfd0334fc3d07592ba9e741dabd1d71..a93b9e4cfac0c21d915f811947f84277715c3328 100644
--- a/components/sync/engine/passive_model_worker.h
+++ b/components/sync/engine/passive_model_worker.h
@@ -6,7 +6,6 @@
 #define COMPONENTS_SYNC_ENGINE_PASSIVE_MODEL_WORKER_H_
 
 #include "base/macros.h"
-#include "components/sync/base/syncer_error.h"
 #include "components/sync/engine/model_safe_worker.h"
 
 namespace syncer {
@@ -22,12 +21,11 @@ class PassiveModelWorker : public ModelSafeWorker {
   ModelSafeGroup GetModelSafeGroup() override;
   bool IsOnModelThread() override;
 
- protected:
-  SyncerError DoWorkAndWaitUntilDoneImpl(const WorkCallback& work) override;
-
  private:
   ~PassiveModelWorker() override;
 
+  void ScheduleWork(base::Closure work) override;
+
   DISALLOW_COPY_AND_ASSIGN(PassiveModelWorker);
 };