file descriptor leak

[zieckey]

EventLoop::watcher_ is a type of PipeEventWatcher, it will create two file descriptors on initialization. We think these two file descriptors whill be closed when PipeEventWatcher destructing :

EventWatcher::~EventWatcher() {
    FreeEvent();
    Close();
}

But when the object is destructing we have no change to call PipeEventWatcher::DoClose() because the drived class PipeEventWatcher must be desctructed before EventWatcher.