Mark postMessage()'s dictionary argument optional

This aligns with IDL requirements. No new tests or implementation bugs as this is roughly equivalent other than the earlier committed version not conforming to IDL.

Fixes #4137.

Author: dtapuska

source

@@ -97575,8 +97575,8 @@ interface <dfn>WorkerGlobalScope</dfn> : <span>EventTarget</span> {
 interface <dfn>DedicatedWorkerGlobalScope</dfn> : <span>WorkerGlobalScope</span> {
   [Replaceable] readonly attribute DOMString <span data-x="dom-DedicatedWorkerGlobalScope-name">name</span>;
 
-  void <span data-x="dom-DedicatedWorkerGlobalScope-postMessage">postMessage</span>(any message, optional sequence&lt;<span data-x="idl-object">object</span>&gt; transfer = []);
-  void <span data-x="dom-DedicatedWorkerGlobalScope-postMessage-options">postMessage</span>(any message, <span>PostMessageOptions</span> options);
+  void <span data-x="dom-DedicatedWorkerGlobalScope-postMessage">postMessage</span>(any message, sequence&lt;<span data-x="idl-object">object</span>&gt; transfer);
+  void <span data-x="dom-DedicatedWorkerGlobalScope-postMessage-options">postMessage</span>(any message, optional <span>PostMessageOptions</span> options);
 
   void <span data-x="dom-DedicatedWorkerGlobalScope-close">close</span>();
 
@@ -98320,8 +98320,8 @@ interface <dfn>SharedWorkerGlobalScope</dfn> : <span>WorkerGlobalScope</span> {
 interface <dfn>Worker</dfn> : <span>EventTarget</span> {
   void <span data-x="dom-Worker-terminate">terminate</span>();
 
-  void <span data-x="dom-Worker-postMessage">postMessage</span>(any message, optional sequence&lt;<span data-x="idl-object">object</span>&gt; transfer = []);
-  void <span data-x="dom-Worker-postMessage-options">postMessage</span>(any message, <span>PostMessageOptions</span> options);
+  void <span data-x="dom-Worker-postMessage">postMessage</span>(any message, sequence&lt;<span data-x="idl-object">object</span>&gt; transfer);
+  void <span data-x="dom-Worker-postMessage-options">postMessage</span>(any message, optional <span>PostMessageOptions</span> options);
   attribute <span>EventHandler</span> <span data-x="handler-Worker-onmessage">onmessage</span>;
   attribute <span>EventHandler</span> <span data-x="handler-Worker-onmessageerror">onmessageerror</span>;
 };