Add compiler error when instantiating abstract class

tests/language/get_set_syntax_test.dart

Index: tests/language/get_set_syntax_test.dart
===================================================================
--- tests/language/get_set_syntax_test.dart	(revision 11549)
+++ tests/language/get_set_syntax_test.dart	(working copy)
@@ -22,7 +22,9 @@
 
 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;
@@ -32,7 +34,9 @@
 
 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;
@@ -41,7 +45,5 @@
 }
 
 main() {
-  new C0();
-  new C1();
-  new C2();
+  new C1();           /// 16: compile-time error
 }