Throw AbstractClassInstantiationError if an abstract class is instantiated

lib/core/errors.dart

 // Copyright (c) 2012, 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.
 
 class AssertionError {
 }
 
 class TypeError extends AssertionError {
 }
 
 class CastException extends TypeError {
 }
 
 class FallThroughError {
   const FallThroughError();
 }
+
+class AbstractClassInstantiationError {
+}