Clarify that is_shared in practice gives access to system libs for am: 81b3f56cab am: 920ec80154 am: 01e7e9ce7c am: 2a52642f3c am: ba4deda74a

Original change: https://android-review.googlesource.com/c/platform/art/+/2214689

Change-Id: I1ccc2e5b2398f04eff7af443f95dbbfb712fb9c9
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>