[Sync] Refactor sync manager into interface.

sync/internal_api/public/sync_manager_factory.h

+// Copyright (c) 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 SYNC_INTERNAL_API_PUBLIC_SYNC_MANAGER_FACTORY_H_
+#define SYNC_INTERNAL_API_PUBLIC_SYNC_MANAGER_FACTORY_H_
+
+#include <string>
+
+#include "base/memory/scoped_ptr.h"
+
+namespace syncer {
+
+class SyncManager;
+
+// Helper class to allow dependency injection of the SyncManager.
+class SyncManagerFactory {
+ public:
+  SyncManagerFactory();
+  virtual ~SyncManagerFactory();
+
+  virtual scoped_ptr<syncer::SyncManager> CreateSyncManager(std::string name);
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(SyncManagerFactory);
+};
+
+}  // namespace syncer
+
+#endif  // SYNC_INTERNAL_API_PUBLIC_SYNC_MANAGER_FACTORY_H_