Optimize out checkInt, checkNum and checkString

tests/compiler/dart2js/mock_libraries.dart

 // Copyright (c) 2014, 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.
 
 // Library for creating mock versions of platform and internal libraries.
 
 library mock_libraries;
 
 const DEFAULT_PLATFORM_CONFIG = """
 [libraries]
@@ skipping 137 matching lines @@
   'buildNamedFunctionType':
       r'''buildNamedFunctionType(returnType, parameterTypes,
                                  namedParameters) {
             return new RuntimeFunctionType();
           }''',
   'checkFunctionSubtype':
       r'''checkFunctionSubtype(var target, String signatureName,
                                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,
                              isStatic, jsArguments, name) {}''',
   'computeSignature':
       'computeSignature(var signature, var context, var contextName) {}',
   'ConstantMap': 'class ConstantMap<K, V> {}',
   'ConstantProtoMap': 'class ConstantProtoMap<K, V> {}',
   'ConstantStringMap': 'class ConstantStringMap<K, V> {}',
   'createInvocationMirror': 'createInvocationMirror(a0, a1, a2, a3, a4, a5) {}',
@@ skipping 285 matching lines @@
 
     const LookupMap(this._entries, [this._nestedMaps = const []])
         : _key = null, _value = null;
 
     const LookupMap.pair(this._key, this._value)
         : _entries = const [], _nestedMaps = const [];
     V operator[](K k) => null;
   }''',
   '_version': 'const _version = "0.0.1+1";',
 };