chrome: Cleanup class/struct forward declarations

chrome/browser/chromeos/session_length_limiter.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_CHROMEOS_SESSION_LENGTH_LIMITER_H_
 #define CHROME_BROWSER_CHROMEOS_SESSION_LENGTH_LIMITER_H_
 
 #include <memory>
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/threading/thread_checker.h"
 #include "base/time/time.h"
 #include "base/timer/timer.h"
 #include "components/prefs/pref_change_registrar.h"
 #include "ui/base/user_activity/user_activity_observer.h"
 
-class PrefService;
 class PrefRegistrySimple;
 
 namespace chromeos {
 
 // Enforces a session length limit by terminating the session when the limit is
 // reached.
 class SessionLengthLimiter : public ui::UserActivityObserver {
  public:
   class Delegate {
    public:
@@ skipping 38 matching lines @@
   std::unique_ptr<base::OneShotTimer> timer_;
   base::TimeTicks session_start_time_;
   bool user_activity_seen_;
 
   DISALLOW_COPY_AND_ASSIGN(SessionLengthLimiter);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_SESSION_LENGTH_LIMITER_H_