Fix typo in native_helper and add dartc test.

tests/language/src/GettersSettersType3Test.dart

Index: tests/language/src/GettersSettersType3Test.dart
diff --git a/tests/language/src/GettersSettersType3Test.dart b/tests/language/src/GettersSettersType3Test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..1ab1082d930f9072f058b80812de0ba9ce17fba2
--- /dev/null
+++ b/tests/language/src/GettersSettersType3Test.dart
@@ -0,0 +1,20 @@
+// Copyright (c) 2012, 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.
+// Getters and setters can have different types, and it is not a warning if the
+// two types are assignable.
+// @static-clean
+
+int bar = 499;
+
+get foo() => bar;
+
+void set foo(String str) { bar = str.length; }
+
+main() {
+  int x = foo;
+  Expect.equals(499, x);
+  foo = "1234";
+  int y = foo;
+  Expect.equals(4, y);
+}