Switch BaseSessionService to use SequencedWorkerPool instead of FILE thread

chrome/browser/sessions/session_service_test_helper.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 CHROME_BROWSER_SESSIONS_SESSION_SERVICE_TEST_HELPER_H_
 #define CHROME_BROWSER_SESSIONS_SESSION_SERVICE_TEST_HELPER_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 52 matching lines @@
                        const SessionTab& session_tab);
 
   void AssertNavigationEquals(
       const sessions::SerializedNavigationEntry& expected,
       const sessions::SerializedNavigationEntry& actual);
 
   void AssertSingleWindowWithSingleTab(
       const std::vector<SessionWindow*>& windows,
       size_t nav_count);
 
-  void set_service(SessionService* service) { service_.reset(service); }
+  void SetService(SessionService* service);
   SessionService* ReleaseService() { return service_.release(); }
   SessionService* service() { return service_.get(); }
 
   SessionBackend* backend();
 
  private:
   scoped_ptr<SessionService> service_;
 
   DISALLOW_COPY_AND_ASSIGN(SessionServiceTestHelper);
 };
 
 #endif  // CHROME_BROWSER_SESSIONS_SESSION_SERVICE_TEST_HELPER_H_