anchor.diff:  
     add(String value) => buffer.write(value);
   
  -  void addError(Object error) { }
  +  void addError(Object error, [StackTrace stackTrace]) { }
   
     void close() { }
   }
  
positive.code: 
    add(String value) { }
  
    void addError(Object error) { }
  
    void close() { }
  
  
negative.code: 
  import 'dart:async';
  import 'dart:html' as html;
  
  // TODO: I would prefer to use a package: import
  import '../sdk/lib/_internal/compiler/compiler.dart' as compiler;
  