[Sync] Make ModelSafeWorker a true interface

chrome/browser/sync/engine/model_safe_worker.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_SYNC_ENGINE_MODEL_SAFE_WORKER_H_
 #define CHROME_BROWSER_SYNC_ENGINE_MODEL_SAFE_WORKER_H_
 #pragma once
 
 #include <map>
 #include <string>
@@ skipping 32 matching lines @@
 
 // The Syncer uses a ModelSafeWorker for all tasks that could potentially
 // modify syncable entries (e.g under a WriteTransaction). The ModelSafeWorker
 // only knows how to do one thing, and that is take some work (in a fully
 // pre-bound callback) and have it performed (as in Run()) from a thread which
 // is guaranteed to be "model-safe", where "safe" refers to not allowing us to
 // cause an embedding application model to fall out of sync with the
 // syncable::Directory due to a race.
 class ModelSafeWorker : public base::RefCountedThreadSafe<ModelSafeWorker> {
  public:
-  ModelSafeWorker();
-  virtual ~ModelSafeWorker();
-
   // Any time the Syncer performs model modifications (e.g employing a
   // WriteTransaction), it should be done by this method to ensure it is done
   // from a model-safe thread.
   virtual UnrecoverableErrorInfo DoWorkAndWaitUntilDone(
-      const WorkCallback& work);
+      const WorkCallback& work) = 0;
 
-  virtual ModelSafeGroup GetModelSafeGroup();
+  virtual ModelSafeGroup GetModelSafeGroup() = 0;
+
+ protected:
+  virtual ~ModelSafeWorker();
 
  private:
   friend class base::RefCountedThreadSafe<ModelSafeWorker>;
-
-  DISALLOW_COPY_AND_ASSIGN(ModelSafeWorker);
 };
 
 // A map that details which ModelSafeGroup each syncable::ModelType
 // belongs to.  Routing info can change in response to the user enabling /
 // disabling sync for certain types, as well as model association completions.
 typedef std::map<syncable::ModelType, ModelSafeGroup>
     ModelSafeRoutingInfo;
 
 // Caller takes ownership of return value.
 base::DictionaryValue* ModelSafeRoutingInfoToValue(
@@ skipping 29 matching lines @@
   virtual void GetModelSafeRoutingInfo(ModelSafeRoutingInfo* out) = 0;
  protected:
   virtual ~ModelSafeWorkerRegistrar() {}
  private:
   DISALLOW_COPY_AND_ASSIGN(ModelSafeWorkerRegistrar);
 };
 
 }  // namespace browser_sync
 
 #endif  // CHROME_BROWSER_SYNC_ENGINE_MODEL_SAFE_WORKER_H_