Make invalid to override method names for local nested functions

tests/compiler/dart2js_extra/immutable_nested_closure_test.dart

Index: tests/compiler/dart2js_extra/immutable_nested_closure_test.dart
diff --git a/tests/compiler/dart2js/dart2js_batch2_run.dart b/tests/compiler/dart2js_extra/immutable_nested_closure_test.dart
similarity index 69%
copy from tests/compiler/dart2js/dart2js_batch2_run.dart
copy to tests/compiler/dart2js_extra/immutable_nested_closure_test.dart
index aee55ef18e5fa77c47bcbf53f5c16125299ed77a..f141c956ca3d83409b68d2000da46e2281064dac 100644
--- a/tests/compiler/dart2js/dart2js_batch2_run.dart
+++ b/tests/compiler/dart2js_extra/immutable_nested_closure_test.dart
@@ -2,9 +2,10 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-@notExisting
-var x;
-
+// Regression test for dartbug.com/19129
 main() {
-  print(x);
+  m() {
+    m = () => 0; /// 01: runtime error
+  }
+  m();
 }