Revert r7729 until Dartium fixes its method override errors.

tests/language/method_override2_test.dart

-// 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.
-
-// Checks that an overriding method has compatible parameters.
-
-interface I {
-  m([a, b]);
-}
-
-interface J extends I { }
-
-interface K extends J {
-  m([c, d]);  /// 00: compile-time error
-}
-
-class C implements I {
-  m([a, b]) {
-    print("$a $b");
-  }
-}
-
-class D
-    extends C  /// 01: compile-time error
-    implements I  /// 02: compile-time error
-    implements J  /// 03: compile-time error
-{
-  m([c, d]) {
-    print("$c $d");
-  }
-}
-
-
-int main() {
-  var c = new C();
-  c.m(a: "hello", b: "world");
-  var d = new D();
-  d.m(c: "hello", d: "world");
-  print("${c is I} ${d is I} ${d is I} ${d is J}");
-}
-