Implement generalized function types.

pkg/compiler/lib/src/parser/element_listener.dart

Index: pkg/compiler/lib/src/parser/element_listener.dart
diff --git a/pkg/compiler/lib/src/parser/element_listener.dart b/pkg/compiler/lib/src/parser/element_listener.dart
index 9420beddbc3f8e55f29884cc7a6abb79540212b5..bcf05c1610b61b24aa8deccfba26ccb24a4d9944 100644
--- a/pkg/compiler/lib/src/parser/element_listener.dart
+++ b/pkg/compiler/lib/src/parser/element_listener.dart
@@ -706,6 +706,9 @@ class ElementListener extends Listener {
 
       case "FASTA_IGNORED":
         return null; // Ignored. This error is already implemented elsewhere.
+
+      default:
+        throw "Unexpected message code: ${message.code}";
     }
     SourceSpan span = reporter.spanFromToken(token);
     reportError(span, errorCode, arguments);