It seems with that flag Proguard modifies the class files in a way that
Dalvik does not like.
Bug: 10307364
Change-Id: If0cc7552da00ae8a3a3a39a9f2f029819ca3164a
So all most commonly-used flags go to proguard_basic_keeps.flags
and they will still be applied when LOCAL_PROGUARD_ENABLED=nosystem.
Bug: 9203442
Change-Id: If018076dc625ac1efe31898b179dbba850218aaf