Migrate test block 47 and downstream dependencies to Dart 2.0.

tests/language_2/checked_null_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.
 
 import "package:expect/expect.dart";
 
 class A {
   Map a;
   Comparator b;
-  // This code exhibited a bug in dart2js checked mode, where the type
-  // of [a] was inferred to be [Comparator] or null;
+  // This code exhibited a bug in dart2js, where the type of [a] was inferred to
+  // be [Comparator] or null;
   A()
       : b = null,
         a = null;
 }
 
 main() {
   Expect.throws(bar); //# 01: continued
 }
 
 bar() {
   // We would create a typed selector for the call to foo, where the
   // receiver type is a typedef. Some code in the dart2js backend were
   // not dealing correctly with typedefs and lead the compiler to
   // crash.
-  new A().a.foo(); //# 01: static type warning
+  new A().a.foo(); //# 01: compile-time error
 }