Merge "Fix use-after-free in async_manager.cc."

        if (!running_) break;

        // wait until time for the next task (if any)

        if (task_queue_.size() > 0) {

          internal_cond_var_.wait_until(guard, (*task_queue_.begin())->time);

          // Make a copy of the time_point because wait_until takes a reference

          // to it and may read it after waiting, by which time the task may

          // have been freed (e.g. via CancelAsyncTask).

          std::chrono::steady_clock::time_point time =

              (*task_queue_.begin())->time;

          internal_cond_var_.wait_until(guard, time);

        } else {

          internal_cond_var_.wait(guard);

        }