Issue #4688, #3595 - Web request use scheduled threads; unit tests terminate

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 50 matching lines @@
     void SetUp()
     {
       webRequest = new TestWebRequest();
       webRequestPtr.reset(webRequest);
 
       eventCallbackCalled = false;
       updateCallbackCalled = false;
       Reset();
     }
 
+    void TearDown()
+    {
+      webRequest->Cancel();
+    }
+
     void Reset()
     {
       jsEngine = CreateJsEngine(appInfo);
       jsEngine->SetLogSystem(AdblockPlus::LogSystemPtr(new LazyLogSystem));
       jsEngine->SetFileSystem(AdblockPlus::FileSystemPtr(new LazyFileSystem));
       jsEngine->SetWebRequest(webRequestPtr);
       jsEngine->SetEventCallback("updateAvailable",
           std::bind(&UpdateCheckTest::EventCallback, this, std::placeholders::_1));
 
       filterEngine.reset(new AdblockPlus::FilterEngine(jsEngine));
@@ skipping 175 matching lines @@
 
   Reset();
   ForceUpdateCheck();
 
   std::this_thread::sleep_for(std::chrono::milliseconds(100));
 
   ASSERT_FALSE(eventCallbackCalled);
   ASSERT_TRUE(updateCallbackCalled);
   ASSERT_FALSE(updateError.empty());
 }