Allow payload_metadata to take raw pointers with size am: 9b8a2bb050 am: 6949831116

Original change: https://android-review.googlesource.com/c/platform/system/update_engine/+/1573381

MUST ONLY BE SUBMITTED BY AUTOMERGER

Change-Id: I4887ae5ead8f94824e8f832e885825ce0e15746f