Update language tests to new optional parameter syntax and semantics.

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]);
+  m({a, b});
 }
 
 interface J extends I { }
 
 interface K extends J {
-  m([c, d]);  /// 00: compile-time error
+  m({c, d});  /// 00: compile-time error
 }
 
 class C implements I {
-  m([a, b]) {
+  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]) {
+  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}");
 }