Skip acquiring block-lock in BumpPointerSpace::AllocThreadUnsafe am: 6aa22c1284 am: b24bb40441 am: c9bca30be1

Original change: https://android-review.googlesource.com/c/platform/art/+/2183095

Change-Id: I1b1a1fd9bb53732dfb7c6912a72bbc9faa442cca
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>