Fix bug #10185976 Black patch displaying in place of drop down spinner across apps

This CL introduced the regression  from https://googleplex-android-review.git.corp.google.com/#/c/336753/

- use "nine-patch" instead of "bitmap" where needed
- fix also a file naming issue

Change-Id: Ib28c3622809e55fc3ed543e6ef34cc3df3421510