Make DatePicker rendering not fail.

Ensures that having a DatePicker in the layout doesn't crash the
complete rendering. The rendering is still not perfect, but at least it
works.

- Return a non-null window token so that ViewPager thinks that it's
  attached to a window and doesn't skip populating the views.
- Fix a style not found issue.

Change-Id: Ied2b71de5b32bcb640bf4ec445e8a39509f800e9