Issue 5013 - Make parameter const ref when applicable.

src/FilterEngine.cpp

Index: src/FilterEngine.cpp
===================================================================
--- a/src/FilterEngine.cpp
+++ b/src/FilterEngine.cpp
@@ -168,17 +168,17 @@
   auto sync = std::make_shared<Sync>();
   auto isConnectionAllowedCallback = params.isConnectionAllowedCallback;
   if (isConnectionAllowedCallback)
     jsEngine->SetIsConnectionAllowedCallback([sync, jsEngine]()->bool
     {
       sync->Wait();
       return jsEngine->IsConnectionAllowed();
     });
-  jsEngine->SetEventCallback("_init", [jsEngine, filterEngine, onCreated, sync, isConnectionAllowedCallback](JsValueList& params)
+  jsEngine->SetEventCallback("_init", [jsEngine, filterEngine, onCreated, sync, isConnectionAllowedCallback](const JsValueList& params)
   {
     filterEngine->firstRun = params.size() && params[0]->AsBool();
     if (isConnectionAllowedCallback)
     {
       std::weak_ptr<FilterEngine> weakFilterEngine = filterEngine;
       jsEngine->SetIsConnectionAllowedCallback([weakFilterEngine, isConnectionAllowedCallback]()->bool
       {
         auto filterEngine = weakFilterEngine.lock();
@@ -427,47 +427,47 @@
 }
 
 JsValuePtr FilterEngine::GetPref(const std::string& pref) const
 {
   JsValuePtr func = jsEngine->Evaluate("API.getPref");
   return std::make_shared<JsValue>(func->Call(*jsEngine->NewValue(pref)));
 }
 
-void FilterEngine::SetPref(const std::string& pref, JsValuePtr value)
+void FilterEngine::SetPref(const std::string& pref, const JsValuePtr& value)
 {
   JsValuePtr func = jsEngine->Evaluate("API.setPref");
   JsConstValueList params;
   params.push_back(jsEngine->NewValue(pref));
   if (value)
     params.push_back(value);
   func->Call(params);
 }
 
 std::string FilterEngine::GetHostFromURL(const std::string& url) const
 {
   JsValuePtr func = jsEngine->Evaluate("API.getHostFromUrl");
   return func->Call(*jsEngine->NewValue(url)).AsString();
 }
 
 void FilterEngine::SetUpdateAvailableCallback(
-    FilterEngine::UpdateAvailableCallback callback)
+    const FilterEngine::UpdateAvailableCallback& callback)
 {
   jsEngine->SetEventCallback("updateAvailable",
       std::bind(&FilterEngine::UpdateAvailable, this, callback,
                 std::placeholders::_1));
 }
 
 void FilterEngine::RemoveUpdateAvailableCallback()
 {
   jsEngine->RemoveEventCallback("updateAvailable");
 }
 
 void FilterEngine::UpdateAvailable(
-    FilterEngine::UpdateAvailableCallback callback, JsValueList& params) const
+    const FilterEngine::UpdateAvailableCallback& callback, const JsValueList& params) const
 {
   if (params.size() >= 1 && !params[0]->IsNull())
     callback(params[0]->AsString());
 }
 
 void FilterEngine::ForceUpdateCheck(
     const FilterEngine::UpdateCheckDoneCallback& callback)
 {
@@ -479,25 +479,25 @@
     jsEngine->SetEventCallback(eventName, std::bind(&FilterEngine::UpdateCheckDone,
       this, eventName, callback, std::placeholders::_1));
     params.push_back(jsEngine->NewValue(eventName));
   }
   func->Call(params);
 }
 
 void FilterEngine::UpdateCheckDone(const std::string& eventName,
-    FilterEngine::UpdateCheckDoneCallback callback, JsValueList& params)
+    const FilterEngine::UpdateCheckDoneCallback& callback, const JsValueList& params)
 {
   jsEngine->RemoveEventCallback(eventName);
 
   std::string error(params.size() >= 1 && !params[0]->IsNull() ? params[0]->AsString() : "");
   callback(error);
 }
 
-void FilterEngine::SetFilterChangeCallback(FilterEngine::FilterChangeCallback callback)
+void FilterEngine::SetFilterChangeCallback(const FilterEngine::FilterChangeCallback& callback)
 {
   jsEngine->SetEventCallback("filterChange", std::bind(&FilterEngine::FilterChanged,
       this, callback, std::placeholders::_1));
 }
 
 void FilterEngine::RemoveFilterChangeCallback()
 {
   jsEngine->RemoveEventCallback("filterChange");
@@ -511,17 +511,17 @@
 std::unique_ptr<std::string> FilterEngine::GetAllowedConnectionType() const
 {
    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(FilterEngine::FilterChangeCallback callback, JsValueList& params) const
+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);
 }
 
 void FilterEngine::ShowNotification(const ShowNotificationCallback& callback,
                                          const JsValueList& params) const