Add MacEfficientFileFlush to testing config.

Bug: 40287434
Change-Id: I985850f8a3c1647be828463f629c1082a413de79
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5383407


Reviewed-by: Olivier Li <olivierli@chromium.org>
Commit-Queue: Francois Pierre Doray <fdoray@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1283273}