| Index: lib/html/scripts/systemhtml.py
 | 
| diff --git a/lib/html/scripts/systemhtml.py b/lib/html/scripts/systemhtml.py
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| index b91a20d1f3bc2bb4b3c44758a0bf070d00c54237..52dc310b3a3e4d0f8e896a06761cb4357935a4d4 100644
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| --- a/lib/html/scripts/systemhtml.py
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| +++ b/lib/html/scripts/systemhtml.py
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| @@ -697,7 +697,7 @@ class Dart2JSBackend(object):
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|          self._members_emitter.Emit(
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|              '\n'
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|              '  void operator[]=(int index, $TYPE value) {\n'
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| -            '    throw new UnsupportedOperationException("Cannot assign element of immutable List.");\n'
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| +            '    throw new StateError("Cannot assign element of immutable List.");\n'
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|              '  }\n',
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|              TYPE=self._NarrowInputType(element_type))
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|  
 | 
| 
 |