Do not require mutator lock for some `ArtField` fields. am: b6e0e02a85 am: 012068f48e

Original change: https://android-review.googlesource.com/c/platform/art/+/2063954

Change-Id: I8767ab176a04a3db009f3ffdf0762b18e82a9c1c
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>