Complain about built-in identifiers.

pkg/front_end/lib/src/fasta/scanner/token.dart

Index: pkg/front_end/lib/src/fasta/scanner/token.dart
diff --git a/pkg/front_end/lib/src/fasta/scanner/token.dart b/pkg/front_end/lib/src/fasta/scanner/token.dart
index bb7efd89bf71e1de9960e0bb0ffaac7969971493..0ff43857119f453627657725b236a51daacb0592 100644
--- a/pkg/front_end/lib/src/fasta/scanner/token.dart
+++ b/pkg/front_end/lib/src/fasta/scanner/token.dart
@@ -126,6 +126,8 @@ abstract class Token {
 
   @override
   bool get isOperator => info.isOperator;
+
+  bool get isBuiltInIdentifier => false;
 }
 
 /**
@@ -177,6 +179,12 @@ class KeywordToken extends Token {
 
   bool isIdentifier() => keyword.isPseudo || keyword.isBuiltIn;
 
+  bool get isBuiltInIdentifier {
+    // TODO(ahe): Remove special case for "deferred" once dartbug.com/29069 is
+    // fixed.
+    return keyword.isBuiltIn || identical("deferred", lexeme);
+  }
+
   String toString() => "KeywordToken($lexeme)";
 }