Change memberName and namedArguments in Invocation to use Symbol.

dart/tests/language/no_such_method_test.dart

 // Copyright (c) 2011, 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.
 // Dart test program testing that NoSuchMethod is properly called.
 
 import "package:expect/expect.dart";
 
 class GetName {
   foo({a, b}) => "foo";
   moo({b}) => "moo";
 }
 
 String getName(im) => im.invokeOn(new GetName());
 
 class NoSuchMethodTest {
 
   foo({a : 10, b : 20}) {
     return (10 * a) + b;
   }
 
   noSuchMethod(Invocation im) {
     Expect.equals("moo", getName(im));
     Expect.equals(0, im.positionalArguments.length);
     Expect.equals(1, im.namedArguments.length);
-    return foo(b:im.namedArguments["b"]);
+    return foo(b:im.namedArguments[const Symbol("b")]);
   }
 
   static testMain() {
     var obj = new NoSuchMethodTest();
     Expect.equals(199, obj.moo(b:99));  // obj.NoSuchMethod called here.
   }
 }
 
 main() {
   NoSuchMethodTest.testMain();
 }