anchor.diff:  
   bool checkFile(String sourcePath) {
     if (!FileSystemEntity.isFileSync(sourcePath)) {
  -    stderr.writeln(
  -        '"$sourcePath" is not a file. See \'--help\' for more information.');
  +    stderr.writeln('"$sourcePath" file not found.');
       stderr.flush();
       return false;
     }
  
positive.code: }
  
  class CompileJSCommand extends DartdevCommand<int> {
    CompileJSCommand() : super('js', 'Compile Dart to JavaScript') {
      argParser
        ..addOption(
          commonOptions['outputFile'].flag,
  
negative.code:     }
      // We expect a single rest argument; the dart entry point.
      if (argResults.rest.length != 1) {
        // This throws.
        usageException('Missing Dart entry point.');
      }
  
      final String sourcePath = argResults.rest[0];
      if (!checkFile(sourcePath)) {
        return -1;
  