Issue 5180 - introduce asynchronous web request

include/AdblockPlus/DefaultWebRequest.h

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2017 eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 #ifndef ADBLOCK_PLUS_DEFAULT_WEB_REQUEST_H
 #define ADBLOCK_PLUS_DEFAULT_WEB_REQUEST_H
 
 #include "WebRequest.h"
 
 namespace AdblockPlus
 {
   /**
    * `WebRequest` implementation that uses `WinInet` on Windows and libcurl
    * on other platforms. A dummy implementation that always reports failure is
    * used if libcurl is not available.
    */
-  class DefaultWebRequest : public WebRequest
+  class DefaultWebRequestSync : public WebRequest
   {
     ServerResponse GET(const std::string& url, const HeaderList& requestHeaders) const;
   };
+
+  class DefaultWebRequest : public IWebRequest
+  {
+  public:
+    explicit DefaultWebRequest(const WebRequestSharedPtr& syncImpl);
+    ~DefaultWebRequest();
+
+    void GET(const std::string& url, const HeaderList& requestHeaders, const GetCallback& getCallback) override;
+  private:
+    WebRequestSharedPtr syncImpl;
+  };
 }
 
 #endif