Only allow load frro drawables from frro directory

Fixes: 383080440
Test: Used test app to verify drawable frros still work
Flag: EXEMPT bugfix
(cherry picked from commit 12e49e7a)
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:b7ae33d3d1fdb14205dea3fa3448afd7309137ac)
Merged-In: I4247e54f3ea0d9e4bf0d9f404e0272751a258ba2
Change-Id: I4247e54f3ea0d9e4bf0d9f404e0272751a258ba2