Issue 5275 - Minimize memory usage as soon as possible

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 247 matching lines @@
     });
   }
   
   jsEngine->SetEventCallback("_init", [jsEngine, filterEngine, onCreated](JsValueList&& params)
   {
     filterEngine->firstRun = params.size() && params[0].AsBool();
     onCreated(filterEngine);
     jsEngine->RemoveEventCallback("_init");
   });
 
+  std::weak_ptr<FilterEngine> weakFilterEngine = filterEngine;
+  filterEngine->SetFilterChangeCallback([weakFilterEngine](const std::string& reason, JsValue&&)
+  {
+    auto filterEngine = weakFilterEngine.lock();
+    if (!filterEngine)
+      return;
+    if (reason == "save")
+      filterEngine->GetJsEngine()->NotifyLowMemory();
+  });
+
   // Lock the JS engine while we are loading scripts, no timeouts should fire
   // until we are done.
   const JsContext context(*jsEngine);
   // Set the preconfigured prefs
   auto preconfiguredPrefsObject = jsEngine->NewObject();
   for (const auto& pref : params.preconfiguredPrefs)
   {
     preconfiguredPrefsObject.SetProperty(pref.first, pref.second);
   }
   jsEngine->SetGlobalProperty("_preconfiguredPrefs", preconfiguredPrefsObject);
@@ skipping 348 matching lines @@
     FilterPtr filter = GetWhitelistingFilter(currentUrl, contentTypeMask, parentUrl);
     if (filter)
     {
       return filter;
     }
     currentUrl = parentUrl;
   }
   while (urlIterator != documentUrls.end());
   return FilterPtr();
 }