anchor.diff:    portraitUp,
   
     /// The orientation that is 90 degrees clockwise from [portraitUp].
  +  ///
  +  /// If the device shows its boot logo in landscape, then the boot logo is
  +  /// shown in [landscapeLeft].
     landscapeLeft,
   
     /// The orientation that is 180 degrees from [portraitUp].
  
positive.code: 
  /// Specifies a particular device orientation.
  ///
  /// Discussion:
  ///
  /// To determine which values correspond to which orientations, first position
  /// the device in its default orientation (this is the orientation that the
  /// system first uses for its boot logo, or the orientation in which the
  /// hardware logos or markings are upright, or the orientation in which the
  /// cameras are at the top). If this is a portrait orientation, then this is
  /// [portraitUp]. Otherwise, it's [landscapeLeft]. As you rotate the device by 90
  /// degrees in a counter-clockwise direction around the axis that traverses the
  /// screen, you step through each value in this enum in the order given. (For a
  /// device with a landscape default orientation, the orientation obtained by
  /// rotating the device 90 degrees clockwise from its default orientation is
  /// [portraitUp].)
  enum DeviceOrientation {
    /// If the device shows its boot logo in portrait, then the boot logo is shown
    /// in [portraitUp]. Otherwise, the device shows its boot logo in landscape
  
negative.code:   return result;
  }
  
  /// Controls specific aspects of the operating system's graphical interface and
  /// how it interacts with the application.
  class SystemChrome {
    SystemChrome._();
  
    /// Specifies the set of orientations the application interface can
    /// be displayed in.
    ///
    /// The `orientation` argument is a list of [DeviceOrientation] enum values.
    /// The empty list is synonymous with having all options enabled.
    static Future<Null> setPreferredOrientations(List<DeviceOrientation> orientations) async {
      await PlatformMessages.invokeMethod(
        _kChannelName,
  