After creating a notification and passing a tag, then subsequent notifications with the same tag don't show up for the entire lifespan of the app.

* Electron version: 1.8.1
* Operating system: Windows 7 x64

### Expected behavior

New notifications should open after the last one has closed.

### Actual behavior

Nothing happens

### How to reproduce

  $ git clone https://github.com/electron/electron-quick-start .
  $ npm install
  $ npm start

Then in the app open dev tools and paste this in the console:

    new Notification("test", { tag: "test" });

Wait for the notification to disappear and paste it again, observe nothingness.
atom/browser/notifications/win/win32_desktop_notifications/toast.cc
}
    }
    if (new_size.cx != this->toast_size_.cx ||
        new_size.cy != this->toast_size_.cy) {
      HDC hdc_screen = GetDC(NULL);
      auto* new_bitmap =
          CreateCompatibleBitmap(hdc_screen, new_size.cx, new_size.cy);
      ReleaseDC(NULL, hdc_screen);
      if (new_bitmap) {
        if (SelectBitmap(hdc_, new_bitmap)) {
          RECT dirty1 = {}, dirty2 = {};
          if (toast_size_.cx < new_size.cx) {
            dirty1 = {toast_size_.cx, 0, new_size.cx, toast_size_.cy};
          }
          if (toast_size_.cy < new_size.cy) {
            dirty2 = {0, toast_size_.cy, new_size.cx, new_size.cy};
          }
          if (this->bitmap_)
            DeleteBitmap(this->bitmap_);
          this->bitmap_ = new_bitmap;
          this->toast_size_ = new_size;
          Invalidate();
          
          
          
          {
            POINT origin = {0, 0};
            UPDATELAYEREDWINDOWINFO ulw;
            ulw.cbSize = sizeof(ulw);
            ulw.hdcDst = NULL;