Fix custom tint showing as disabled pre-Lollipop

Also unifies the contract that we expect for button
tinting: if a developer provides a tint they are
responsible for all of it (including the disabled tint).

Test: included
BUG: 31303357

Change-Id: I7f654d7dcd3f7c99ce4bab754eb447eb45e1322f
6 files changed