components: Cleanup class/struct fwd declarations

components/update_client/update_client_internal.h

 // Copyright 2015 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_UPDATE_CLIENT_UPDATE_CLIENT_INTERNAL_H_
 #define COMPONENTS_UPDATE_CLIENT_UPDATE_CLIENT_INTERNAL_H_
 
 #include <memory>
 #include <queue>
 #include <set>
 #include <string>
 #include <vector>
 
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/observer_list.h"
 #include "base/threading/thread_checker.h"
 #include "components/update_client/crx_downloader.h"
 #include "components/update_client/update_checker.h"
 #include "components/update_client/update_client.h"
 
-namespace base {
-class SequencedTaskRunner;
-class SingleThreadTaskRunner;
-}  // namespace base
-
 namespace update_client {
 
 class Configurator;
 class PingManager;
 class Task;
 class UpdateEngine;
 enum class Error;
-struct TaskContext;
 
 class UpdateClientImpl : public UpdateClient {
  public:
   UpdateClientImpl(const scoped_refptr<Configurator>& config,
                    std::unique_ptr<PingManager> ping_manager,
                    UpdateChecker::Factory update_checker_factory,
                    CrxDownloader::Factory crx_downloader_factory);
 
   // Overrides for UpdateClient.
   void AddObserver(Observer* observer) override;
@@ skipping 45 matching lines @@
   std::unique_ptr<UpdateEngine> update_engine_;
 
   base::ObserverList<Observer> observer_list_;
 
   DISALLOW_COPY_AND_ASSIGN(UpdateClientImpl);
 };
 
 }  // namespace update_client
 
 #endif  // COMPONENTS_UPDATE_CLIENT_UPDATE_CLIENT_INTERNAL_H_