Fix thread-safety-analysis warning on Clang r484197 am: 788d46a488

Original change: https://android-review.googlesource.com/c/platform/art/+/2385813

Change-Id: I044627a871f0cc735a2a167aa564d87c5059494d
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>