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Change-Id: I0a8e23f3ac5c7e0d3b63ebd3e7381d531ca86ad5

third_party/dart-sdk/sdk/pkg/dartpad/lib/src/sandbox.dart

diff --git a/third_party/dart-sdk/sdk/pkg/dartpad/lib/src/sandbox.dart b/third_party/dart-sdk/sdk/pkg/dartpad/lib/src/sandbox.dart
index 67a8358..d078895 100644
--- a/third_party/dart-sdk/sdk/pkg/dartpad/lib/src/sandbox.dart
+++ b/third_party/dart-sdk/sdk/pkg/dartpad/lib/src/sandbox.dart
@@ -274,8 +274,10 @@
     ).toJS;
     container.appendChild(iframe);
 
+    final parentWindow = container.ownerDocument?.defaultView ?? web.window;
+
     return await Future(() async {
-      await for (final event in web.window.onMessage) {
+      await for (final event in parentWindow.onMessage) {
         if (event.source != iframe.contentWindow ||
             !event.data.isA<JSObject>()) {
           continue;