report abstract as extraneous modifier

pkg/front_end/lib/src/fasta/parser/parser.dart

Index: pkg/front_end/lib/src/fasta/parser/parser.dart
diff --git a/pkg/front_end/lib/src/fasta/parser/parser.dart b/pkg/front_end/lib/src/fasta/parser/parser.dart
index d3bcceae05a50ab1bdd7ec486e4fa479814c7fa3..725cb2871e2cb57cb66975e27a5d62cb7e24e1e2 100644
--- a/pkg/front_end/lib/src/fasta/parser/parser.dart
+++ b/pkg/front_end/lib/src/fasta/parser/parser.dart
@@ -2059,7 +2059,6 @@ class Parser {
       }
       int order = modifierOrder(token);
       if (order < 3) {
-        // `abstract` isn't parsed with this method.
         if (order > currentOrder) {
           currentOrder = order;
           if (optional("var", token)) {
@@ -2149,6 +2148,11 @@ class Parser {
               token, fasta.templateExtraneousModifier);
           token = token.next;
         }
+      } else if (order == 3) {
+        assert(optional('abstract', token));
+        reportRecoverableErrorWithToken(
+            token, fasta.templateExtraneousModifier);
+        token = token.next;
       } else {
         break;
       }