Have setters use strict -> like methods

pkg/dev_compiler/test/codegen/language/field_override4_test.dart

 // Copyright (c) 2013, 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 we report a compile-time error when an instance field conflicts
 // with an inherited instance method of the same name.
 
 import "package:expect/expect.dart";
 
 class A {
   var foo = 42;  /// 00: ok
   get foo => 42;  /// 01: ok
   foo() => 42;  /// 02: compile-time error
   set foo(value) { }  /// 03: ok
 }
 
 class B extends A {
-  var foo = 42;
+  dynamic foo = 42;
 }
 
 main() {
   Expect.equals(42, new B().foo);
 }