Optimize out checkInt, checkNum and checkString

tests/compiler/dart2js/mock_libraries.dart

Index: tests/compiler/dart2js/mock_libraries.dart
diff --git a/tests/compiler/dart2js/mock_libraries.dart b/tests/compiler/dart2js/mock_libraries.dart
index 4ceb37586757212d7bd8ae34b8f1a72bb9d2be37..867bf4d37667db8cb4d99606e024461e5afbf6f0 100644
--- a/tests/compiler/dart2js/mock_libraries.dart
+++ b/tests/compiler/dart2js/mock_libraries.dart
@@ -155,6 +155,9 @@ const Map<String, String> DEFAULT_JS_HELPER_LIBRARY = const <String, String>{
                                String contextName, var context,
                                var typeArguments) {}''',
   'checkMalformedType': 'checkMalformedType(value, message) {}',
+  'checkInt': 'checkInt(value) {}',
+  'checkNum': 'checkNum(value) {}',
+  'checkString': 'checkString(value) {}',
   'Closure': 'abstract class Closure implements Function { }',
   'closureFromTearOff':
       r'''closureFromTearOff(receiver, functions, reflectionInfo,