Add CoreClasses

pkg/compiler/lib/src/js_emitter/program_builder/field_visitor.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.
 
 part of dart2js.js_emitter.program_builder;
 
 /**
  * [member] is a field (instance, static, or top level).
  *
  * [name] is the field name that the [Namer] has picked for this field's
@@ skipping 147 matching lines @@
       // knowing that it is there.  Therefore we don't need to use a getter
       // (that will throw if the getter method is missing), but can always
       // access the field directly.
       field is ClosureFieldElement;
   }
 
   bool canAvoidGeneratedCheckedSetter(VariableElement member) {
     // We never generate accessors for top-level/static fields.
     if (!member.isInstanceMember) return true;
     DartType type = member.type;
-    return type.treatAsDynamic || (type.element == compiler.objectClass);
+    return type.treatAsDynamic || type.isObject;
   }
 }