Do not require mutator lock for some `ArtField` fields.

Namely for `access_flags_` and `offset_`. The `ArtField` has
not been a managed heap object for a very long time, so we
do not need to guard these primitive fields with the mutator
lock. And we similarly do not require the mutator lock for
`ArtMethod::access_flags_` either.

Test: Rely on TreeHugger.
Change-Id: I6522dad83089a742131e6e8689db04a19bd30ead
1 file changed