Remove unused API.

dart/tests/compiler/dart2js/exit_code_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 the exit code of dart2js in case of exceptions, fatal errors, errors,
 // warnings, etc.
 
 
 import 'dart:async';
 import 'dart:io' show Platform;
@@ skipping 177 matching lines @@
   });
 }
 
 Future testExitCodes(String marker, Map<String,int> expectedExitCodes) {
   return Future.forEach(expectedExitCodes.keys, (String type) {
     return testExitCode(marker, type, expectedExitCodes[type]);
   });
 }
 
 void main() {
+  bool isCheckedMode = false;
+  assert(isCheckedMode = true);
+  Expect.isTrue(isCheckedMode, 'This test must be run in checked mode.');
+
   const beforeRun = const {
     '': 0,
     'NoSuchMethodError': 253,
     'assert': 253,
     'invariant': 253
   };
 
   const duringRun = const {
     '': 0,
     'NoSuchMethodError': 253,
@@ skipping 15 matching lines @@
 
   asyncStart();
   Future.forEach(tests.keys, (marker) {
     return testExitCodes(marker, tests[marker]);
   }).then((_) {
     Expect.equals(beforeRun.length * 2 + duringRun.length * 4,
                   checkedResults);
     asyncEnd();
   });
 }