Make Client.postMessage to unloaded client not throw

cf834f0
clarified the target object can be null, and it must throw in that case.

But #1291 pointed out that we
cannot implement that behavior without blocking the service worker
process in multi-process browser architectures.

This change makes the control return right away if the target client has
been unloaded.

Fixes #1291.

docs/index.bs

@@ -1028,10 +1028,11 @@ spec: webappsec-referrer-policy; urlPrefix: https://w3c.github.io/webappsec-refe
       The <dfn method for="Client"><code>postMessage(|message|, |transfer|)</code></dfn> method *must* run these steps:
 
         1. Let |sourceSettings| be the <a>context object</a>'s <a>relevant settings object</a>.
-        1. Let |destination| be the {{ServiceWorkerContainer}} object whose [=ServiceWorkerContainer/service worker client=] is the <a>context object</a>'s [=Client/service worker client=], or null if no match is found.
-        1. If |destination| is null, <a>throw</a> an "{{InvalidStateError}}" {{DOMException}}.
         1. Let |serializeWithTransferResult| be <a abstract-op>StructuredSerializeWithTransfer</a>(|message|, |transfer|). Rethrow any exceptions.
-        1. Add a <a>task</a> that runs the following steps to |destination|'s [=ServiceWorkerContainer/client message queue=]:
+        1. Let |targetClient| be the [=context object=]'s [=Client/service worker client=], or null if it does not exist (i.e. if the [=/service worker client=] has been [=Handle Service Worker Client Unload|unloaded=]).
+        1. If |targetClient| is null, return.
+        1. Let |destination| be |targetClient|'s {{ServiceWorkerContainer}} object (i.e. the {{ServiceWorkerContainer}} object's [=relevant settings object=] is |targetClient|).
+        1. Add a [=task=] that runs the following steps to |destination|'s [=ServiceWorkerContainer/client message queue=]:
             1. Let |origin| be the [=Unicode serialization of an origin|Unicode serialization=] of |sourceSettings|'s [=environment settings object/origin=].
             1. Let |source| be a {{ServiceWorker}} object, which represents the [=ServiceWorkerGlobalScope/service worker=] associated with |sourceSettings|'s [=environment settings object/global object=].
             1. Let |deserializeRecord| be <a abstract-op>StructuredDeserializeWithTransfer</a>(|serializeWithTransferResult|, |destination|'s [=relevant Realm=]).
@@ -1087,7 +1088,7 @@ spec: webappsec-referrer-policy; urlPrefix: https://w3c.github.io/webappsec-refe
     <section algorithm="client-navigate">
       <h4 id="client-navigate">{{WindowClient/navigate(url)}}</h4>
 
-      The <dfn method for="WindowClient"><code>navigate()</code></dfn> method *must* run these steps:
+      The <dfn method for="WindowClient"><code>navigate(|url|)</code></dfn> method *must* run these steps:
 
         1. Let |url| be the result of <a lt="URL parser">parsing</a> |url| with the <a>context object</a>'s <a>relevant settings object</a>'s <a>API base URL</a>.
         1. If |url| is failure, return a <a>promise</a> rejected with a <code>TypeError</code>.

docs/v1/index.bs

@@ -966,10 +966,11 @@ spec: webappsec-referrer-policy; urlPrefix: https://w3c.github.io/webappsec-refe
       The <dfn method for="Client"><code>postMessage(|message|, |transfer|)</code></dfn> method *must* run these steps:
 
         1. Let |sourceSettings| be the <a>context object</a>'s <a>relevant settings object</a>.
-        1. Let |destination| be the {{ServiceWorkerContainer}} object whose [=ServiceWorkerContainer/service worker client=] is the <a>context object</a>'s [=Client/service worker client=], or null if no match is found.
-        1. If |destination| is null, <a>throw</a> an "{{InvalidStateError}}" {{DOMException}}.
         1. Let |serializeWithTransferResult| be <a abstract-op>StructuredSerializeWithTransfer</a>(|message|, |transfer|). Rethrow any exceptions.
-        1. Add a <a>task</a> that runs the following steps to |destination|'s [=ServiceWorkerContainer/client message queue=]:
+        1. Let |targetClient| be the [=context object=]'s [=Client/service worker client=], or null if it does not exist (i.e. if the [=/service worker client=] has been [=Handle Service Worker Client Unload|unloaded=]).
+        1. If |targetClient| is null, return.
+        1. Let |destination| be |targetClient|'s {{ServiceWorkerContainer}} object (i.e. the {{ServiceWorkerContainer}} object's [=relevant settings object=] is |targetClient|).
+        1. Add a [=task=] that runs the following steps to |destination|'s [=ServiceWorkerContainer/client message queue=]:
             1. Let |origin| be the [=Unicode serialization of an origin|Unicode serialization=] of |sourceSettings|'s [=environment settings object/origin=].
             1. Let |source| be a {{ServiceWorker}} object, which represents the [=ServiceWorkerGlobalScope/service worker=] associated with |sourceSettings|'s [=environment settings object/global object=].
             1. Let |deserializeRecord| be <a abstract-op>StructuredDeserializeWithTransfer</a>(|serializeWithTransferResult|, |destination|'s [=relevant Realm=]).
@@ -1025,7 +1026,7 @@ spec: webappsec-referrer-policy; urlPrefix: https://w3c.github.io/webappsec-refe
     <section algorithm="client-navigate">
       <h4 id="client-navigate">{{WindowClient/navigate(url)}}</h4>
 
-      The <dfn method for="WindowClient"><code>navigate()</code></dfn> method *must* run these steps:
+      The <dfn method for="WindowClient"><code>navigate(|url|)</code></dfn> method *must* run these steps:
 
         1. Let |url| be the result of <a lt="URL parser">parsing</a> |url| with the <a>context object</a>'s <a>relevant settings object</a>'s <a>API base URL</a>.
         1. If |url| is failure, return a <a>promise</a> rejected with a <code>TypeError</code>.