Issue #3593 - Make isolate a fully internal member of the engine

test/UpdateCheck.cpp

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2016 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 44 matching lines @@
       jsEngine->SetWebRequest(webRequest);
       jsEngine->SetEventCallback("updateAvailable",
         std::bind(&UpdateCheckTest::EventCallback, this, std::placeholders::_1));
 
       filterEngine = std::make_shared<AdblockPlus::FilterEngine>(jsEngine);
     }
 
     void Destroy()
     {
       webRequest->Cancel();
+      eventCallbackParams.clear();
       filterEngine.reset();
       ToInternal(jsEngine)->WaitForQuietScheduler();
+      ASSERT_EQ(1, jsEngine.use_count());
       jsEngine.reset();
-      ASSERT_EQ(0, jsEngine.use_count());
     }
 
   protected:
     AdblockPlus::AppInfo appInfo;
     std::shared_ptr<TestWebRequest> webRequest;
     AdblockPlus::JsEnginePtr jsEngine;
     FilterEnginePtr filterEngine;
 
     bool eventCallbackCalled;
     AdblockPlus::JsValueList eventCallbackParams;
@@ skipping 196 matching lines @@
 
   Reset();
   ForceUpdateCheck();
 
   std::this_thread::sleep_for(std::chrono::milliseconds(100));
 
   ASSERT_FALSE(eventCallbackCalled);
   ASSERT_TRUE(updateCallbackCalled);
   ASSERT_FALSE(updateError.empty());
 }