Issue 5013 - Make parameter const ref when applicable.

src/Utils.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 11 matching lines @@
 #include <cctype>
 #include <functional>
 #include <istream>
 #include <string>
 #include <v8.h>
 
 namespace AdblockPlus
 {
   namespace Utils
   {
-    std::string Slurp(const std::istream& stream);
+    std::string Slurp(std::istream& stream);
     std::string FromV8String(const v8::Handle<v8::Value>& value);
     v8::Local<v8::String> ToV8String(v8::Isolate* isolate, const std::string& str);
 
     // Code for templated function has to be in a header file, can't be in .cpp
     template<class T>
     T TrimString(const T& text)
     {
       // Via http://stackoverflow.com/questions/216823/whats-the-best-way-to-trim-stdstring
       T trimmed(text);
       trimmed.erase(trimmed.begin(), std::find_if(trimmed.begin(), trimmed.end(), std::not1(std::ptr_fun<int, int>(std::isspace))));
       trimmed.erase(std::find_if(trimmed.rbegin(), trimmed.rend(), std::not1(std::ptr_fun<int, int>(std::isspace))).base(), trimmed.end());
       return trimmed;
     }
 #ifdef _WIN32
     std::wstring ToUtf16String(const std::string& str);
     std::string ToUtf8String(const std::wstring& str);
     std::wstring CanonizeUrl(const std::wstring& url);
 #endif
   }
 }
 
 #endif