Migrate test block 47 and downstream dependencies to Dart 2.0.

tests/language_2/checked_setter_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 implicit setters in checked mode do a type check.
 
 import "package:expect/expect.dart";
 
 class A {
   C c;
 }
 
 class B extends A {}
 
 class C {}
 
 var array = [new B()];
 
 main() {
   array[0].c = new C();
-  bool inCheckedMode = false;
-  try {
-    var i = 42;
-    String a = i;
-  } catch (e) {
-    inCheckedMode = true;
-  }
-  if (inCheckedMode) {
-    Expect.throws(() => array[0].c = new B(), (e) => e is TypeError);
-  }
+  array[0].c = new B(); /*@compile-error=unspecified*/
 }