Issue 5013 - Make parameter const ref when applicable.

src/FilterEngine.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 502 matching lines @@
    auto prefValue = GetPref("allowed_connection_type");
    if (prefValue->AsString().empty())
      return nullptr;
    return std::unique_ptr<std::string>(new std::string(prefValue->AsString()));
 }
 
 void FilterEngine::FilterChanged(const FilterEngine::FilterChangeCallback& callback, const JsValueList& params) const
 {
   std::string action(params.size() >= 1 && !params[0]->IsNull() ? params[0]->AsString() : "");
   JsValuePtr item(params.size() >= 2 ? params[1] : jsEngine->NewValue(false));
-  callback(action, item);
+  callback(action, *item);
 }
 
 void FilterEngine::ShowNotification(const ShowNotificationCallback& callback,
                                          const JsValueList& params) const
 {
   if (params.size() < 1)
     return;
 
   if (!params[0]->IsObject())
   {
@@ skipping 40 matching lines @@
     FilterPtr filter = GetWhitelistingFilter(currentUrl, contentTypeMask, parentUrl);
     if (filter)
     {
       return filter;
     }
     currentUrl = parentUrl;
   }
   while (urlIterator != documentUrls.end());
   return FilterPtr();
 }