Worker changes to prepare for lock-free shutdown.

chrome/browser/sync/glue/history_model_worker.h

Index: chrome/browser/sync/glue/history_model_worker.h
diff --git a/chrome/browser/sync/glue/history_model_worker.h b/chrome/browser/sync/glue/history_model_worker.h
index 6eb42c05b1517db6a45eb4806b1e8c2adcb220d4..93112ab2035393cc9c0027675d990477db427bdb 100644
--- a/chrome/browser/sync/glue/history_model_worker.h
+++ b/chrome/browser/sync/glue/history_model_worker.h
@@ -13,6 +13,7 @@
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
 #include "chrome/browser/common/cancelable_request.h"
+#include "chrome/browser/history/history_db_task.h"
 #include "chrome/browser/history/history_service.h"
 
 class HistoryService;
@@ -24,13 +25,17 @@ namespace browser_sync {
 class HistoryModelWorker : public syncer::ModelSafeWorker {
  public:
   explicit HistoryModelWorker(
-      const base::WeakPtr<HistoryService>& history_service);
+      const base::WeakPtr<HistoryService>& history_service,
+      syncer::WorkerLoopDestructionObserver* observer);
 
   // syncer::ModelSafeWorker implementation. Called on syncapi SyncerThread.
-  virtual syncer::SyncerError DoWorkAndWaitUntilDone(
-      const syncer::WorkCallback& work) OVERRIDE;
+  virtual void RegisterForLoopDestruction() OVERRIDE;
   virtual syncer::ModelSafeGroup GetModelSafeGroup() OVERRIDE;
 
+ protected:
+  virtual syncer::SyncerError DoWorkAndWaitUntilDoneImpl(
+      const syncer::WorkCallback& work) OVERRIDE;
+
  private:
   virtual ~HistoryModelWorker();