Add compiler error when instantiating abstract class

tests/language/get_set_syntax_test.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.
 
 var get;
 var get a;            /// 00: compile-time error
 var get b, c;         /// 01: compile-time error
 
 var set;
 var set d;            /// 02: compile-time error
 var set e, f;         /// 03: compile-time error
 
 class C0 {
   var get;
   var get a;          /// 04: compile-time error
   var get b, c;       /// 05: compile-time error
 
   var set;
   var set d;          /// 06: compile-time error
   var set e, f;       /// 07: compile-time error
 }
 
 class C1 {
   List get;
-  List get a;         /// 08: compile-time error
+  List get a;
+  abstract List get a2;
+  abstract List get a3 => null;  /// 08: compile-time error
   List get b, c;      /// 09: compile-time error
 
   List set;
   List set d;         /// 10: compile-time error
   List set e, f;      /// 11: compile-time error
 }
 
 class C2 {
   List<int> get;
-  List<int> get a;    /// 12: compile-time error
+  List<int> get a;
+  abstract List<int> get a2;
+  abstract List<int> get a3 => null;  /// 08: compile-time error
   List<int> get b, c; /// 13: compile-time error
 
   List<int> set;
   List<int> set d;    /// 14: compile-time error
   List<int> set e, f; /// 15: compile-time error
 }
 
 main() {
-  new C0();
-  new C1();
-  new C2();
+  new C1();           /// 16: compile-time error
 }