Refactor the UpdateEngine and its actions in the component updater.

components/update_client/action.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_H_
-#define COMPONENTS_UPDATE_CLIENT_ACTION_H_
-
-#include <stddef.h>
-
-#include <string>
-
-#include "base/callback.h"
-#include "base/macros.h"
-#include "base/threading/thread_checker.h"
-#include "components/update_client/crx_update_item.h"
-#include "components/update_client/update_client.h"
-
-namespace update_client {
-
-enum class Error;
-struct CrxUpdateItem;
-struct UpdateContext;
-
-// Any update can be broken down as a sequence of discrete steps, such as
-// checking for updates, downloading patches, updating, and waiting between
-// successive updates. An action is the smallest unit of work executed by
-// the update engine.
-//
-// Defines an abstract interface for a unit of work, executed by the
-// update engine as part of an update.
-class Action {
- public:
-  virtual ~Action() {}
-
-  // Runs the code encapsulated by the action. When an action completes, it can
-  // chain up and transfer the execution flow to another action or it can
-  // invoke the |callback| when this function has completed and there is nothing
-  // else to do.
-  virtual void Run(UpdateContext* update_context, Callback callback) = 0;
-};
-
-// Provides a reusable implementation of common functions needed by actions.
-class ActionImpl {
- protected:
-  ActionImpl();
-  ~ActionImpl();
-
-  void Run(UpdateContext* update_context, Callback callback);
-
-  // Changes the current state of the |item| to the new state |to|.
-  void ChangeItemState(CrxUpdateItem* item, CrxUpdateItem::State to);
-
-  // Changes the state of all items in |update_context_|. Returns the count
-  // of items affected by the call.
-  size_t ChangeAllItemsState(CrxUpdateItem::State from,
-                             CrxUpdateItem::State to);
-
-  // Returns the item associated with the component |id| or nullptr in case
-  // of errors.
-  CrxUpdateItem* FindUpdateItemById(const std::string& id) const;
-
-  void NotifyObservers(UpdateClient::Observer::Events event,
-                       const std::string& id);
-
-  // Updates the CRX at the front of the CRX queue in this update context.
-  void UpdateCrx();
-
-  // Completes updating the CRX at the front of the queue, and initiates
-  // the update for the next CRX in the queue, if the queue is not empty.
-  void UpdateCrxComplete(CrxUpdateItem* item);
-
-  // Called when the updates for all CRXs have finished and the execution
-  // flow must return back to the update engine.
-  void UpdateComplete(Error error);
-
-  base::ThreadChecker thread_checker_;
-
-  UpdateContext* update_context_;  // Not owned by this class.
-  Callback callback_;
-
- private:
-  DISALLOW_COPY_AND_ASSIGN(ActionImpl);
-};
-
-}  // namespace update_client
-
-#endif  // COMPONENTS_UPDATE_CLIENT_ACTION_H_