[Notice Framework] Move OnEventOccured to DesktopViewManagerInterface

This will allow the WebUI side to use the passed in interface to the
handler, to call OnEventOccurred.

Bug: 322163208
Change-Id: I1b240012cb44c320755b9dca02baa8f9371c30a4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6542429
Reviewed-by: Abe Boujane <boujane@google.com>
Commit-Queue: Jacob Stanley <jacobstanley@google.com>
Reviewed-by: Christine Ying <chrstne@google.com>
Cr-Commit-Position: refs/heads/main@{#1460063}