Fix task concurrency in components/update_client

components/update_client/update_engine.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_ENGINE_H_
 #define COMPONENTS_UPDATE_CLIENT_UPDATE_ENGINE_H_
 
 #include <list>
 #include <queue>
 #include <set>
@@ skipping 35 matching lines @@
                           const std::string& id)>;
   using CrxDataCallback = UpdateClient::CrxDataCallback;
 
   UpdateEngine(const scoped_refptr<Configurator>& config,
                UpdateChecker::Factory update_checker_factory,
                CrxDownloader::Factory crx_downloader_factory,
                PingManager* ping_manager,
                const NotifyObserversCallback& notify_observers_callback);
   ~UpdateEngine();
 
-  // Returns true is the CRX identified by the given |id| is being updated.
-  bool IsUpdating(const std::string& id) const;
-
   bool GetUpdateState(const std::string& id, CrxUpdateItem* update_state);
 
   void Update(bool is_foreground,
               const std::vector<std::string>& ids,
               const UpdateClient::CrxDataCallback& crx_data_callback,
               const CompletionCallback& update_callback);
 
  private:
   void UpdateComplete(UpdateContext* update_context, int error);
 
@@ skipping 67 matching lines @@
   // TODO(sorin): use a map instead of vector.
   std::vector<CrxUpdateItem*> update_items;
 
   // Contains the ids of the items to update.
   std::queue<std::string> queue;
 };
 
 }  // namespace update_client
 
 #endif  // COMPONENTS_UPDATE_CLIENT_UPDATE_ENGINE_H_