Remove unused variables.

chrome/browser/chromeos/arc/arc_service_launcher.h

 // Copyright 2016 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_CHROMEOS_ARC_ARC_SERVICE_LAUNCHER_H_
 #define CHROME_BROWSER_CHROMEOS_ARC_ARC_SERVICE_LAUNCHER_H_
 
 #include <memory>
 
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
-#include "base/threading/thread_checker.h"
 #include "components/arc/arc_service_manager.h"
 
 namespace arc {
 
 // Detects ARC availability and launches ARC bridge service.
 class ArcServiceLauncher {
  public:
   ArcServiceLauncher();
   ~ArcServiceLauncher();
 
   void Initialize();
   void Shutdown();
 
  private:
   // DBus callback.
   void OnArcAvailable(bool available);
 
-  base::ThreadChecker thread_checker_;
   std::unique_ptr<ArcServiceManager> arc_service_manager_;
   base::WeakPtrFactory<ArcServiceLauncher> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ArcServiceLauncher);
 };
 
 }  // namespace arc
 
 #endif  // CHROME_BROWSER_CHROMEOS_ARC_ARC_SERVICE_LAUNCHER_H_