Abstract methods aren't implementations.

We should only be checking the visibility of actual implementations
of interface methods. Intervening abstract methods are allowed to
be non-public.

Bug: https://code.google.com/p/android/issues/detail?id=42991
Change-Id: I510d0cc6c1f89d161d4ebad7ef058c03fa09e9b0
Merge remote-tracking branch 'slim/jb4.2' into mirage