Optimize out checkInt, checkNum and checkString

pkg/compiler/lib/src/js_backend/backend_helpers.dart

 // Copyright (c) 2015, 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 dart2js.js_backend.helpers;
 
 import '../common.dart';
 import '../common/names.dart' show Identifiers, Uris;
 import '../common/resolution.dart' show Resolution;
 import '../compiler.dart' show Compiler;
@@ skipping 439 matching lines @@
       cachedCheckConcurrentModificationError =
           findHelper('checkConcurrentModificationError');
     }
     return cachedCheckConcurrentModificationError;
   }
 
   Element get throwConcurrentModificationError {
     return findHelper('throwConcurrentModificationError');
   }
 
+  Element get checkInt => _checkInt ??= findHelper('checkInt');
+  Element _checkInt;
+
+  Element get checkNum => _checkNum ??= findHelper('checkNum');
+  Element _checkNum;
+
+  Element get checkString => _checkString ??= findHelper('checkString');
+  Element _checkString;
+
   Element get stringInterpolationHelper {
     return findHelper('S');
   }
 
   Element get wrapExceptionHelper {
     return findHelper(r'wrapException');
   }
 
   Element get throwExpressionHelper {
     return findHelper('throwExpression');
@@ skipping 233 matching lines @@
   MethodElement _objectNoSuchMethod;
 
   MethodElement get objectNoSuchMethod {
     if (_objectNoSuchMethod == null) {
       _objectNoSuchMethod =
           coreClasses.objectClass.lookupLocalMember(Identifiers.noSuchMethod_);
     }
     return _objectNoSuchMethod;
   }
 }