[DevTools] Add ReportingApiReportUpdated event to CDP

Inform DevTools about updates to ReportingReports by sending a CDP event
on every change.

Bug: 1205856
Change-Id: I44c14c43001708192ef1ac7683d2ed0a7c83b19f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3136533


Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Reviewed-by: Yutaka Hirano <yhirano@chromium.org>
Commit-Queue: Wolfgang Beyer <wolfi@chromium.org>
Cr-Commit-Position: refs/heads/main@{#918755}