Clarify the format and assumptions on the dex file locations. am: 949c197585 am: 42187d5886

Original change: https://android-review.googlesource.com/c/platform/art/+/2969535

Change-Id: I3a1cc3a90a35596369d65c93d4024e6930b63186
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>