Broken references in Web Background Synchronization

[dontcallmedom-bot]

While crawling Web Background Synchronization, the following links to other specifications were detected as pointing to non-existing anchors, which should be fixed:

• https://notifications.spec.whatwg.org/#permission-model
• https://slightlyoff.github.io/ServiceWorker/spec/service_worker/index.html#service-worker-registration-interface
• https://slightlyoff.github.io/ServiceWorker/spec/service_worker/index.html#service-worker-global-scope-interface
• https://slightlyoff.github.io/ServiceWorker/spec/service_worker/index.html#extendable-event-interface
• https://slightlyoff.github.io/ServiceWorker/spec/service_worker/index.html#dfn-extend-lifetime-promises

_{This issue was detected and reported semi-automatically by Strudy based on data collected in webref.}