anchor.diff:  
   enum NamingScope {
     global,
  -  instance
  +  instance,
  +  constant
   }
positive.code:   final Map<String, jsAst.Name> userInstanceOperators =
        new HashMap<String, jsAst.Name>();
  
    Set<String> getUsedNames(NamingScope scope) {
      if (scope == NamingScope.global) {
        return usedGlobalNames;
      } else {
        assert(scope == NamingScope.instance);
        return usedInstanceNames;
      }
    }
  
  
negative.code:     jsAst.Name result = constantNames[constant];
      if (result == null) {
        String longName = constantLongName(constant);
        result = getFreshName(NamingScope.constant, longName);
        constantNames[constant] = result;
      }
      return result;
  