Issue 5013 - Make parameter const ref when applicable.

include/AdblockPlus/DefaultFileSystem.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
@@ skipping 20 matching lines @@
   /**
    * `FileSystem` implementation that interacts directly with the operating
    * system's file system.
    * All paths are considered relative to the base path, or to the current
    * working directory if no base path is set (see `SetBasePath()`).
    */
   class DefaultFileSystem : public FileSystem
   {
   public:
     std::shared_ptr<std::istream> Read(const std::string& path) const;
-    void Write(const std::string& path, const std::istream& data);
+    void Write(const std::string& path, std::istream& data);
     void Move(const std::string& fromPath, const std::string& toPath);
     void Remove(const std::string& path);
     StatResult Stat(const std::string& path) const;
     std::string Resolve(const std::string& path) const;
 
     /**
      * Sets the base path, all paths are considered relative to it.
      * @param path Base path.
      */
     void SetBasePath(const std::string& path);
 
   protected:
     std::string basePath;
   };
 }
 
 #endif