[Sync] Move thread checking into the ModelSafeWorker interface.

components/sync/engine/model_safe_worker.h

 // Copyright 2012 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 COMPONENTS_SYNC_ENGINE_MODEL_SAFE_WORKER_H_
 #define COMPONENTS_SYNC_ENGINE_MODEL_SAFE_WORKER_H_
 
 #include <map>
 #include <memory>
 #include <string>
@@ skipping 46 matching lines @@
   // If not stopped, call DoWorkAndWaitUntilDoneImpl() to do work. Otherwise
   // return CANNOT_DO_WORK.
   SyncerError DoWorkAndWaitUntilDone(const WorkCallback& work);
 
   // Soft stop worker by setting stopped_ flag. Called when sync is disabled
   // or browser is shutting down. Called on UI loop.
   virtual void RequestStop();
 
   virtual ModelSafeGroup GetModelSafeGroup() = 0;
 
+  // Returns true if called on the thread this worker works on.
+  virtual bool IsOnModelThread() = 0;
+
  protected:
   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 SyncerError DoWorkAndWaitUntilDoneImpl(const WorkCallback& work) = 0;
 
   // Return true if the worker was stopped. Thread safe.
@@ skipping 21 matching lines @@
     const ModelSafeRoutingInfo& routing_info);
 
 ModelTypeSet GetRoutingInfoTypes(const ModelSafeRoutingInfo& routing_info);
 
 ModelSafeGroup GetGroupForModelType(const ModelType type,
                                     const ModelSafeRoutingInfo& routes);
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_ENGINE_MODEL_SAFE_WORKER_H_