Fix crash in deferred_constraint_constants_test.

pkg/compiler/lib/src/compile_time_constants.dart

Index: pkg/compiler/lib/src/compile_time_constants.dart
diff --git a/pkg/compiler/lib/src/compile_time_constants.dart b/pkg/compiler/lib/src/compile_time_constants.dart
index b739ce5deb6ab38a1ee6e412c14e48d63354edd6..f5876d8d495fc08127bbaec7def20f9fc9333615 100644
--- a/pkg/compiler/lib/src/compile_time_constants.dart
+++ b/pkg/compiler/lib/src/compile_time_constants.dart
@@ -982,7 +982,7 @@ class CompileTimeConstantEvaluator extends Visitor<AstConstant> {
       error(node, message);
 
       return new AstConstant(
-          null, node, new NullConstantExpression(new NullConstantValue()));
+          null, node, new ErroneousConstantExpression());
     }
     // Else we don't need to do anything. The final handler is only
     // optimistically trying to compile constants. So it is normal that we