Restructure parser error handling and recovery.

pkg/fasta/lib/src/source/diet_parser.dart

Index: pkg/fasta/lib/src/source/diet_parser.dart
diff --git a/pkg/fasta/lib/src/source/diet_parser.dart b/pkg/fasta/lib/src/source/diet_parser.dart
index 5f1640a64a4df470f2bdffac5c53c25a7eb56fd8..0c52154cbb0c4c053718b81722b615bde34a9c36 100644
--- a/pkg/fasta/lib/src/source/diet_parser.dart
+++ b/pkg/fasta/lib/src/source/diet_parser.dart
@@ -31,10 +31,10 @@ class DietParser extends ClassMemberParser {
     listener.beginOptionalFormalParameters(token);
     if (!optional('(', token)) {
       if (optional(';', token)) {
-        listener.reportError(token, ErrorKind.ExpectedOpenParens);
+        reportRecoverableError(token, ErrorKind.ExpectedOpenParens, {});
         return token;
       }
-      return listener.unexpected(token);
+      return reportUnrecoverableError(token, ErrorKind.UnexpectedToken);
     }
     BeginGroupToken beginGroupToken = token;
     Token endToken = beginGroupToken.endGroup;