| Index: lib/src/compiler/js_field_storage.dart
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| diff --git a/lib/src/compiler/js_field_storage.dart b/lib/src/compiler/js_field_storage.dart
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| index 29b5a77a67e7c72438a33d665d6091da1679a69a..b66d41c6cc214c9c6474caa038ba93acf75c5d35 100644
 | 
| --- a/lib/src/compiler/js_field_storage.dart
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| +++ b/lib/src/compiler/js_field_storage.dart
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| @@ -23,7 +23,7 @@ PropertyOverrideResult checkForPropertyOverride(FieldElement field,
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|  
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|    for (var superclass in superclasses) {
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|      // Stop if we reach a native type.
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| -    if (extensionTypes.contains(superclass)) break;
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| +    if (extensionTypes.isNativeClass(superclass)) break;
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|  
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|      var superprop = getProperty(superclass, field.library, field.name);
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|      if (superprop == null) continue;
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| 
 |