anchor.diff:  
     // Report size and scanning time again. See discussion above.
     if (old != scanTotalChars) print('input size changed? ${old} chars');
  -  report("Scanner", scanTimer.elapsedMicroseconds);
  +  report("scan", scanTimer.elapsedMicroseconds);
   
     var pTime = parseTimer.elapsedMicroseconds - scanTimer.elapsedMicroseconds;
  -  report("Parser", pTime);
  +  report("parse", pTime);
   }
   
   /// Add to [files] all sources reachable from [start].
  
positive.code:   if (!files.add(start)) return;
    var unit = parseDirectives(start);
    for (var directive in unit.directives) {
      if (directive is! UriBasedDirective) continue;
      var next = sources.resolveUri(start, directive.uri.stringValue);
      collectSources(next, files);
    }
  }
  
  
negative.code: 
    print('input size: ${scanTotalChars} chars');
    var loadTime = loadTimer.elapsedMicroseconds - scanTimer.elapsedMicroseconds;
    report("load", loadTime);
    report("scan", scanTimer.elapsedMicroseconds);
    return files;
  }
  
  