Convert between Dart and JavaScript SerializedScriptValues on postMessage.

lib/html/dart2js/html_dart2js.dart

Index: lib/html/dart2js/html_dart2js.dart
diff --git a/lib/html/dart2js/html_dart2js.dart b/lib/html/dart2js/html_dart2js.dart
index daf6e9f2bd4d3297f67c603f436870f009198038..2dcb62407bc3b1b6b481b9792afe07e5e738eba5 100644
--- a/lib/html/dart2js/html_dart2js.dart
+++ b/lib/html/dart2js/html_dart2js.dart
@@ -9624,7 +9624,18 @@ class _DedicatedWorkerContextImpl extends _WorkerContextImpl implements Dedicate
   _DedicatedWorkerContextEventsImpl get on =>
     new _DedicatedWorkerContextEventsImpl(this);
 
-  void postMessage(Object message, [List messagePorts]) native;
+  void postMessage(message, [messagePorts]) {
+    if (?messagePorts) {
+      var message_1 = _convertDartToNative_SerializedScriptValue(message);
+      _postMessage_1(message_1, messagePorts);
+      return;
+    }
+    var message_2 = _convertDartToNative_SerializedScriptValue(message);
+    _postMessage_2(message_2);
+    return;
+  }
+  void _postMessage_1(message, List messagePorts) native "postMessage";
+  void _postMessage_2(message) native "postMessage";
 }
 
 class _DedicatedWorkerContextEventsImpl extends _WorkerContextEventsImpl implements DedicatedWorkerContextEvents {
@@ -19225,7 +19236,8 @@ abstract class MessageEvent implements Event {
 
 class _MessageEventImpl extends _EventImpl implements MessageEvent native "*MessageEvent" {
 
-  final Object data;
+  Dynamic get data => _convertNativeToDart_SerializedScriptValue(this._data);
+  Dynamic get _data() native "return this.data;";
 
   final String lastEventId;
 
@@ -19288,7 +19300,18 @@ class _MessagePortImpl extends _EventTargetImpl implements MessagePort native "*
 
   bool $dom_dispatchEvent(_EventImpl evt) native "dispatchEvent";
 
-  void postMessage(Object message, [List messagePorts]) native;
+  void postMessage(message, [messagePorts]) {
+    if (?messagePorts) {
+      var message_1 = _convertDartToNative_SerializedScriptValue(message);
+      _postMessage_1(message_1, messagePorts);
+      return;
+    }
+    var message_2 = _convertDartToNative_SerializedScriptValue(message);
+    _postMessage_2(message_2);
+    return;
+  }
+  void _postMessage_1(message, List messagePorts) native "postMessage";
+  void _postMessage_2(message) native "postMessage";
 
   void $dom_removeEventListener(String type, EventListener listener, [bool useCapture]) native "removeEventListener";
 
@@ -36532,7 +36555,23 @@ class _WindowImpl extends _EventTargetImpl implements Window native "@*DOMWindow
 
   _DatabaseImpl openDatabase(String name, String version, String displayName, int estimatedSize, [DatabaseCallback creationCallback]) native;
 
-  void postMessage(message, String targetOrigin, [List messagePorts]) native;
+  void postMessage(message, String targetOrigin, [messagePorts]) {
+    if (?message &&
+        !?messagePorts) {
+      var message_1 = _convertDartToNative_SerializedScriptValue(message);
+      _postMessage_1(message_1, targetOrigin);
+      return;
+    }
+    if (?message &&
+        (messagePorts is List || messagePorts === null)) {
+      var message_2 = _convertDartToNative_SerializedScriptValue(message);
+      _postMessage_2(message_2, targetOrigin, messagePorts);
+      return;
+    }
+    throw const Exception("Incorrect number or type of arguments");
+  }
+  void _postMessage_1(message, targetOrigin) native "postMessage";
+  void _postMessage_2(message, targetOrigin, List messagePorts) native "postMessage";
 
   void print() native;
 
@@ -36894,7 +36933,18 @@ class _WorkerImpl extends _AbstractWorkerImpl implements Worker native "*Worker"
   _WorkerEventsImpl get on =>
     new _WorkerEventsImpl(this);
 
-  void postMessage(message, [List messagePorts]) native;
+  void postMessage(message, [messagePorts]) {
+    if (?messagePorts) {
+      var message_1 = _convertDartToNative_SerializedScriptValue(message);
+      _postMessage_1(message_1, messagePorts);
+      return;
+    }
+    var message_2 = _convertDartToNative_SerializedScriptValue(message);
+    _postMessage_2(message_2);
+    return;
+  }
+  void _postMessage_1(message, List messagePorts) native "postMessage";
+  void _postMessage_2(message) native "postMessage";
 
   void terminate() native;
 }
@@ -39430,6 +39480,12 @@ _convertDartToNative_SerializedScriptValue(value) {
   return _convertDartToNative_PrepareForStructuredClone(value);
 }
 
+// May modify original.  If so, action is idempotent.
+_convertNativeToDart_SerializedScriptValue(object) {
+  return _convertNativeToDart_AcceptStructuredClone(object);
+}
+
+
 
 /**
  * Converts a Dart value into a JavaScript SerializedScriptValue.  Returns the