Merge "Execute DelayedCallback outside CallbackScheduler lock"

void CallbackScheduler::loop() {

    while (true) {

        std::lock_guard<std::mutex> lock(mMutex);

        std::unique_lock<std::mutex> lock(mMutex);

        if (mFinished) {

            // Destructor was called, so let the callback thread die.

            break;

        }

        while (!mQueue.empty() && mQueue.top().isExpired()) {

            mQueue.top().run();

            DelayedCallback callback = mQueue.top();

            mQueue.pop();

            lock.unlock();

            callback.run();

            lock.lock();

        }

        if (mQueue.empty()) {

            // Wait until a new callback is scheduled.