components: Cleanup class/struct fwd declarations

components/update_client/action_update.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_ACTION_UPDATE_H_
 #define COMPONENTS_UPDATE_CLIENT_ACTION_UPDATE_H_
 
 #include <map>
 #include <memory>
 #include <string>
 #include <vector>
 
 #include "base/macros.h"
 #include "base/threading/thread_checker.h"
 #include "base/version.h"
 #include "components/update_client/action.h"
 #include "components/update_client/component_unpacker.h"
 #include "components/update_client/crx_downloader.h"
 #include "components/update_client/update_client.h"
 #include "components/update_client/update_engine.h"
 #include "url/gurl.h"
 
 namespace base {
 class FilePath;
 }
 
 namespace update_client {
 
-class UpdateChecker;
 enum class UnpackError;
 
 // Defines a template method design pattern for ActionUpdate. This class
 // implements the common code for updating a single CRX using either
 // a differential or a full update algorithm.
 // TODO(sorin): further refactor this class to enforce that there is a 1:1
 // relationship between one instance of this class and one CRX id. In other
 // words, make the CRX id and its associated CrxUpdateItem data structure
 // a member of this class instead of passing them around as function parameters.
 class ActionUpdate : public Action, protected ActionImpl {
@@ skipping 119 matching lines @@
                       ErrorCategory error_category,
                       int error,
                       int extended_error) override;
 
   DISALLOW_COPY_AND_ASSIGN(ActionUpdateFull);
 };
 
 }  // namespace update_client
 
 #endif  // COMPONENTS_UPDATE_CLIENT_ACTION_UPDATE_H_