Sync model_prototyping.proto to Chrome.

This CL was generated by a Copybara workflow. See the attached bug for more details.

Bug: b/363029050
BbcpOrigin-RevId: 669327407
Change-Id: I3962ab041062b266cef777e82278630aa74b414a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5824675


Reviewed-by: Ryan Sturm <ryansturm@chromium.org>
Commit-Queue: Ryan Sturm <ryansturm@chromium.org>
Auto-Submit: Max Curran <curranmax@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1349428}