Make background helper's API 21 workaround more permissive

Currently it only works when the background is
a GradientDrawable. Since unwrapping drawable containers
is unpleasant, we'll just apply the workaround all the
time.

BUG: 27674299
Change-Id: Id6fb5f8185f2d07129fb93acbf932550162bc902
1 file changed