Tidy up CardView's background handling

- Moved the CardViewDelegate instance to be a member
  variable. Allows us to actually hide implementation
  methods.
- Removed some methods from the Delegate which are no
  longer needed.
- Allow CardView's background to work with
  DrawableCompat.setTint calls
- Fixed an issue with DrawableCompat where we would NPE
  if setTint*() was called before mutate()ing the drawable.

BUG: 26478024

Change-Id: I01162774fe193a0c9a6f9ab266f117e0a940dee5
6 files changed