components: Cleanup class/struct fwd declarations

components/domain_reliability/service.h

 // Copyright 2014 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 COMPONENTS_DOMAIN_RELIABILITY_SERVICE_H_
 #define COMPONENTS_DOMAIN_RELIABILITY_SERVICE_H_
 
 #include <memory>
 #include <string>
 
 #include "base/callback_forward.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/single_thread_task_runner.h"
 #include "components/domain_reliability/clear_mode.h"
 #include "components/domain_reliability/domain_reliability_export.h"
 #include "components/keyed_service/core/keyed_service.h"
 
 class GURL;
-class PrefService;
 
 namespace base {
 class Value;
 }  // namespace base
 
 namespace net {
 class URLRequestContextGetter;
 }  // namespace net
 
 namespace domain_reliability {
@@ skipping 36 matching lines @@
  protected:
   DomainReliabilityService();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(DomainReliabilityService);
 };
 
 }  // namespace domain_reliability
 
 #endif  // COMPONENTS_DOMAIN_RELIABILITY_SERVICE_H_