Extensions: Ignore old registration requests in ServiceWorkerTaskQueue

ServiceWorkerTaskQueue asynchronously verifies the service worker
registration. After verification, it decides if the worker must be
re-registered.

This change ensures that the re-registration is not triggered if the
extension was deactivated (e.g. for a reload) while the verification
was in-progress.

Any old requests should be dropped to avoid multiple registration
requests. If the old requests are not dropped, it can also cause a
crash if the new version of the extension doesn't have a service
worker (and we try to register it).

Bug: 391414854
Change-Id: Ifd8418145b3a17693687172d77b794a4bd38a4a6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6169822
Commit-Queue: Sohail Rajdev <sorajdev@microsoft.com>
Reviewed-by: Emilia Paz <emiliapaz@chromium.org>
Reviewed-by: Justin Lulejian <jlulejian@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1410036}