plumb id to webidl layer

Author: wanderview

docs/index.bs

@@ -122,7 +122,9 @@ spec: webappsec-referrer-policy; urlPrefix: https://w3c.github.io/webappsec-refe
 }
 </pre>
 
+<!-- TODO: expose getRegistrationById() -->
 <!-- TODO: uncontrol old clients that no longer match in Activate -->
+<!-- TODO: change scope logic -->
 
 <section>
   <h2 id="motivations">Motivations</h2>
@@ -216,7 +218,7 @@ spec: webappsec-referrer-policy; urlPrefix: https://w3c.github.io/webappsec-refe
 
     A [=/service worker registration=] has an associated <dfn export id="dfn-origin">origin</dfn> an [=environment settings object/origin=].
 
-    A [=/service worker registration=] has an associated <dfn export id="dfn-id">id</dfn>.  It is initially set to null.
+    A [=/service worker registration=] has an associated <dfn export id="dfn-id">id</dfn> a [=DOMString=].  It is initially set to null.
 
     A [=/service worker registration=] has an associated <dfn export id="dfn-installing-worker">installing worker</dfn> (a [=/service worker=] or null) whose [=service worker/state=] is "`installing`". It is initially set to null.
 
@@ -509,6 +511,7 @@ spec: webappsec-referrer-policy; urlPrefix: https://w3c.github.io/webappsec-refe
         readonly attribute ServiceWorker? active;
         [SameObject] readonly attribute NavigationPreloadManager navigationPreload;
 
+        readonly attribute DOMString id;
         readonly attribute USVString scope;
         readonly attribute ServiceWorkerUpdateViaCache updateViaCache;
 
@@ -581,6 +584,12 @@ spec: webappsec-referrer-policy; urlPrefix: https://w3c.github.io/webappsec-refe
       The <dfn attribute for="ServiceWorkerRegistration"><code>navigationPreload</code></dfn> getter steps are to return the [=ServiceWorkerRegistration/service worker registration=]'s {{NavigationPreloadManager}} object.
     </section>
 
+    <section algorithm="service-worker-registration-id">
+      <h4 id="service-worker-registration-id">{{ServiceWorkerRegistration/id}}</h4>
+
+      The <dfn attribute for="ServiceWorkerRegistration"><code>id</code></dfn> getter steps are to return the [=ServiceWorkerRegistration/service worker registration=]'s [=service worker registration/id=].
+    </section>
+
     <section algorithm="service-worker-registration-scope">
       <h4 id="service-worker-registration-scope">{{ServiceWorkerRegistration/scope}}</h4>
 
@@ -697,6 +706,7 @@ spec: webappsec-referrer-policy; urlPrefix: https://w3c.github.io/webappsec-refe
     </pre>
     <pre class="idl" id="registration-option-list-dictionary">
       dictionary RegistrationOptions {
+        DOMString id;
         USVString scope;
         WorkerType type = "classic";
         ServiceWorkerUpdateViaCache updateViaCache = "imports";