tweak fasta parser event debug code

pkg/front_end/lib/src/fasta/source/outline_builder.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library fasta.outline_builder;
 
 import 'package:kernel/ast.dart' show ProcedureKind;
 
 import '../../scanner/token.dart' show Token;
 
@@ skipping 960 matching lines @@
         }
         buffer.write(lexeme);
       }
       docToken = docToken.next;
     }
     return buffer.toString();
   }
 
   @override
   void debugEvent(String name) {
-    // printEvent(name);
+    // printEvent('OutlineBuilder: $name');
   }
 }