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 d86c385bb685670587f37f5ba9e566127d014155..23f9e3a15a66443b6c418cdf549c8b96b9fbd05e 100644
--- a/pkg/front_end/lib/src/fasta/parser/parser.dart
+++ b/pkg/front_end/lib/src/fasta/parser/parser.dart
@@ -887,6 +887,32 @@ class Parser {
     if (!token.isIdentifier()) {
       token =
           reportUnrecoverableError(token, ErrorKind.ExpectedIdentifier)?.next;
+    } else if (token.isBuiltInIdentifier) {
+      // It is a compile-time error if a built-in identifier is used as the
+      // declared name of a prefix, class, type parameter or type alias.
+      // It is a compile-time error to use a built-in identifier other than
+      // dynamic as a type annotation or type parameter.
+      switch (context) {
+        case IdentifierContext.importPrefixDeclaration:
+        case IdentifierContext.typedefDeclaration:
+        case IdentifierContext.enumDeclaration:
+        case IdentifierContext.namedMixinDeclaration:
+        case IdentifierContext.classDeclaration:
+        case IdentifierContext.typeVariableDeclaration:
+          reportRecoverableError(
+              token, ErrorKind.BuiltInIdentifierInDeclaration);
+          break;
+
+        case IdentifierContext.typeReference:
+        case IdentifierContext.typeReferenceContinuation:
+          if (!optional("dynamic", token)) {
+            reportRecoverableError(token, ErrorKind.BuiltInIdentifierAsType);
+          }
+          break;
+
+        default:
+          break;
+      }
     }
     listener.handleIdentifier(token, context);
     return token.next;