Complain about built-in identifiers.

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 e2083093cd49b0be62fa52fe6a554097d106a296..6f5aea713804530b6f381faae1e712561b70550d 100644
--- a/pkg/front_end/lib/src/fasta/parser/parser.dart
+++ b/pkg/front_end/lib/src/fasta/parser/parser.dart
@@ -887,6 +887,13 @@ class Parser {
     if (!token.isIdentifier()) {
       token =
           reportUnrecoverableError(token, ErrorKind.ExpectedIdentifier)?.next;
+    } else if (token.isBuiltInIdentifier &&
+        !context.isBuiltInIdentifierAllowed) {
+      if (context.inDeclaration) {
+        reportRecoverableError(token, ErrorKind.BuiltInIdentifierInDeclaration);
+      } else if (!optional("dynamic", token)) {
+        reportRecoverableError(token, ErrorKind.BuiltInIdentifierAsType);
+      }
     }
     listener.handleIdentifier(token, context);
     return token.next;