Add regression test for issue 20074.

tests/language/regress_20074_test.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // 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.
 
-class A {
-  static const S = 'A.S';
-}
+// Regression test for issue 20074. Check that a parameter is not declared
+// in the same scope as its function declaration.
 
-const S = 'S';
-
-foo(var p) {
-  switch (p) {
-    case S:
-      break;
-    case A.S:
-      break;
-    case 'abc':
-      break;
+doit() {
+  error(error) {
+    print(error);
   }
+  error('foobar');
 }
 
 main() {
-  foo('p');
-}
+  doit();
+}