[Extensions] Service worker registration status histograms fixes.

Revived metrics:
  Extensions.ServiceWorkerBackground.RegistrationStatus
  Extensions.ServiceWorkerBackground.RegistrationMismatchMitigated
  Extensions.ServiceWorkerBackground.RegistrationMismatchLocation

New metric:
  Extensions.ServiceWorkerBackground.Registration_FailStatus

Service worker registration is critical for detecting when a worker is
ready to receive an event. Other metrics indicate that registration is
a potential cause of start worker failures so this data will help
determine if there's an issue on registration, or if it might happen
afterwards.

Registration_FailStatus is added to determine why the registration is
failed, similar to what is done with worker start.

Also converts the emits to functions vs macros per the style guide.

Bug: 40909770
Change-Id: Ibea35760c59b4336a52650522fc8012cda169dca
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5406144


Commit-Queue: Justin Lulejian <jlulejian@chromium.org>
Reviewed-by: David Bertoni <dbertoni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1283510}