Create the JavaScript constructor dynamically.

frog/tests/leg/class_codegen_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.
 // Test that parameters keep their names in the output.
 
 #import("compiler_helper.dart");
 #import("parser_helper.dart");
 
 final String TEST_ONE = @"""
 class A { }
@@ skipping 63 matching lines @@
     Expect.isTrue(generated.contains(@'Isolate.$defineClass("B", "A"'));
   }
 
   checkOutput(compileAll(TEST_TWO));
   checkOutput(compileAll(TEST_THREE));
 }
 
 fieldTest() {
   String generated = compileAll(TEST_FOUR);
   Expect.isTrue(generated.contains(@"""
-Isolate.$defineClass("B", "A", function B(z, y, A_x) {
-  this.z = z;
-  this.y = y;
-  this.x = A_x;
- },"""));
+Isolate.$defineClass("B", "A", ["z", "y", "x"],"""));
 }
 
 constructor1() {
   String generated = compileAll(TEST_FIVE);
   Expect.isTrue(generated.contains(@"new $.A(x);"));
 }
 
 main() {
   twoClasses();
   subClass();
   fieldTest();
   constructor1();
 }