Address Peter's comments in https://codereview.chromium.org/11361059, and fix a host-checked mode b…

tests/language/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.
 
 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;
   A() : b = null, a = null;
 }
 
 main() { 
-  Expect.throws(bar, (e) => e is NullPointerException);
+  Expect.throws(bar);
 }
 
 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();
 }