Bugfix in html_dart2js: Detect window objects in a way compatible with cross domain iframes

dart/tools/dom/src/dart2js_Conversions.dart

Index: dart/tools/dom/src/dart2js_Conversions.dart
diff --git a/dart/tools/dom/src/dart2js_Conversions.dart b/dart/tools/dom/src/dart2js_Conversions.dart
index 41b624e6c2e4be2e647bee146edf7983e9a68017..e56d389fd89b920dc9c3e4e8a7589b88b05fcf69 100644
--- a/dart/tools/dom/src/dart2js_Conversions.dart
+++ b/dart/tools/dom/src/dart2js_Conversions.dart
@@ -20,10 +20,10 @@ EventTarget _convertNativeToDart_EventTarget(e) {
   if (e == null) {
     return null;
   }
-  // Assume it's a Window if it contains the setInterval property.  It may be
+  // Assume it's a Window if it contains the postMessage property.  It may be
   // from a different frame - without a patched prototype - so we cannot
   // rely on Dart type checking.
-  if (JS('bool', r'"setInterval" in #', e)) {
+  if (JS('bool', r'"postMessage" in #', e)) {
     var window = _DOMWindowCrossFrame._createSafe(e);
     // If it's a native window.
     if (window is EventTarget) {