Issue 5013 - Make parameter const ref when applicable.

src/DefaultFileSystem.cpp

 /*
  * 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 58 matching lines @@
 std::shared_ptr<std::istream>
 DefaultFileSystem::Read(const std::string& path) const
 {
   std::shared_ptr<std::istream> result(new std::ifstream(NormalizePath(path).c_str()));
   if (result->fail())
     throw RuntimeErrorWithErrno("Failed to open " + path);
   return result;
 }
 
 void DefaultFileSystem::Write(const std::string& path,
-                              const std::istream& data)
+                              std::istream& data)
 {
   std::ofstream file(NormalizePath(path).c_str(), std::ios_base::out | std::ios_base::binary);
   file << Utils::Slurp(data);
 }
 
 void DefaultFileSystem::Move(const std::string& fromPath,
                              const std::string& toPath)
 {
   if (rename(NormalizePath(fromPath).c_str(), NormalizePath(toPath).c_str()))
     throw RuntimeErrorWithErrno("Failed to move " + fromPath + " to " + toPath);
@@ skipping 97 matching lines @@
 void DefaultFileSystem::SetBasePath(const std::string& path)
 {
   basePath = path;
 
   if (*basePath.rbegin() == PATH_SEPARATOR)
   {
     basePath.resize(basePath.size() - 1);
   }
 }