Add an about flag for the predictable reported quota change.

Bug: 369865059
Change-Id: I417b483afb1b217c0d42b02a5a6b3c4f553ef7dc
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5983389


Reviewed-by: Evan Stade <estade@chromium.org>
Reviewed-by: Ayu Ishii <ayui@chromium.org>
Commit-Queue: Reema A <reemaa@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1378953}