Testing ResourcesCompat.getDrawableForDensity

* Added unthemed and theme-aware tests for getDrawableForDensity
(with major caveats discussed in the linked bug).
* Switched order of existing assertEquals() calls for the correct
order of expected and actual values.

Bug: 25931811
Change-Id: Ica5056e93ea3761dc9bb47c0b4b7d4af048d6806
14 files changed