Constant sparkle scale

Drawables from different themes are yielding different densities.
Framework themes are returning 160 (DENSITY_MEDIUM), while AppCompat
is reporting 420 (DENSITY_420.)

This is causing the sparkles to have completely different sizes on
the same device, which is wrong.

Fixes: 189236372
Test: manual
Change-Id: Ia79e360123cf740aaba85d5348f07604c2b39026