Use designated initializers for ActorOverlayStruct

Bug: 447114657
Change-Id: Ib4953c119a550b5c48b94671623d4bd1e2f782e6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7002495
Auto-Submit: Abe Boujane <boujane@google.com>
Commit-Queue: Abe Boujane <boujane@google.com>
Reviewed-by: Jacob Stanley <jacobstanley@google.com>
Commit-Queue: Christine Ying <chrstne@google.com>
Reviewed-by: Christine Ying <chrstne@google.com>
Cr-Commit-Position: refs/heads/main@{#1524226}