anchor.diff:  
     parseCommandLine(handlers, argv);
   
  +  if (wantHelp) helpAndExit(verbose);
  +
     if (arguments.isEmpty()) {
       helpAndFail('Error: No Dart file specified.');
     }
  
positive.code:   Uri out = cwd.resolve('out.js');
    List<String> options = new List<String>();
    bool explicitOut = false;
  
    passThrough(String argument) => options.add(argument);
  
  
negative.code:   // terminal size normally 80x24. Two lines are used for the prompts
    // before and after running the compiler.
    print('''
  Usage: dart2js [options] dartfile
  
  Compiles Dart to JavaScript.
  
  Common options:
    -o<file> Generate the output into <file>.
    -c       Insert runtime type checks and enable assertions (checked mode).
    -h       Display this message (add -v for information about all options).''');
  }
  
  void verboseHelp() {
    print('''
  Usage: dart2js [options] dartfile
  
  Compiles Dart to JavaScript.
  
  Supported options:
    -o<file>, --out=<file>
      Generate the output into <file>.
  
    -c, --enable-checked-mode, --checked
      Insert runtime type checks and enable assertions (checked mode).
  
    -h, /h, /?, --help
      Display this message (add -v for information about all options).
  
    -v, --verbose
      Display verbose information.
  
    --suppress-warnings
      Do not display any warnings.
  
    --no-colors
      Do not add colors to diagnostic messages.
  
  The following options are only used for compiler development and may
  be removed in a future version:
    --throw-on-error
      Throw an exception if a compile-time error is detected.
  
    --library-root=<directory>
      Where to find the Dart platform libraries.
  
    --allow-mock-compilation
      Do not generate a call to main if either of the following
      libraries are used: dart:dom, dart:html dart:io.''');
  }
  
  void helpAndExit(bool verbose) {
    if (verbose) {
      verboseHelp();
    } else {
      help();
    }
    exit(0);
  }
  
  