Issue 5082 - fix possible race condition in DefaultTimer

src/DefaultTimer.h

 /*
 * 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
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
 */
 
 #ifndef ADBLOCK_PLUS_DEFAULT_TIMER_H
 #define ADBLOCK_PLUS_DEFAULT_TIMER_H
 
 #include <AdblockPlus/ITimer.h>
 #include <mutex>
 #include <condition_variable>
 #include <queue>
-#include <atomic>
 #include <thread>
 
 namespace AdblockPlus
 {
   class DefaultTimer : public ITimer
   {
     struct TimerUnit
     {
       std::chrono::steady_clock::time_point fireAt;
       TimerCallback callback;
@@ skipping 10 matching lines @@
   public:
     DefaultTimer();
     ~DefaultTimer();
     void SetTimer(const std::chrono::milliseconds& timeout, const TimerCallback& timerCallback) override;
   private:
     void ThreadFunc();
   private:
     std::mutex mutex;
     std::condition_variable conditionVariable;
     TimerUnits timers;
-    std::atomic<bool> shouldThreadStop;
+    bool shouldThreadStop;
     std::thread m_thread;
   };
 }
 
 #endif