anchor.diff:    /// be null.
     ImageShader(Image image, TileMode tmx, TileMode tmy, Float64List matrix4) {
       if (image == null)
  -      throw new ArgumentError("[image] argument cannot be null");
  +      throw new ArgumentError('"image" argument cannot be null.');
       if (tmx == null)
  -      throw new ArgumentError("[tmx] argument cannot be null");
  +      throw new ArgumentError('"tmx" argument cannot be null.');
       if (tmy == null)
  -      throw new ArgumentError("[tmy] argument cannot be null");
  +      throw new ArgumentError('"tmy" argument cannot be null.');
       if (matrix4 == null)
  -      throw new ArgumentError("[matrix4] argument cannot be null");
  +      throw new ArgumentError('"matrix4" argument cannot be null.');
       if (matrix4.length != 16)
  -      throw new ArgumentError("[matrix4] must have 16 entries.");
  +      throw new ArgumentError('"matrix4" must have 16 entries.');
       _constructor();
       _initWithImage(image, tmx.index, tmy.index, matrix4);
     }
  
positive.code:     List<int> indices,
    }) {
      if (textureCoordinates != null && textureCoordinates.length != positions.length)
        throw new ArgumentError("[positions] and [textureCoordinates] lengths must match");
      if (colors != null && colors.length != positions.length)
        throw new ArgumentError("[positions] and [colors] lengths must match");
      if (indices != null && indices.any((int i) => i < 0 || i >= positions.length))
        throw new ArgumentError("[indices] values must be valid indices in the positions list");
  
      Float32List encodedPositions = _encodePointList(positions);
      Float32List encodedTexs = (textureCoordinates != null) ?
        _encodePointList(textureCoordinates) : null;
      Int32List encodedColors = (colors != null) ? _encodeColorList(colors) : null;
      Int32List encodedIndices = (indices != null) ? new Int32List.fromList(indices) : null;
  
      _constructor();
      _init(mode.index, encodedPositions, encodedTexs, encodedColors, encodedIndices);
    }
  
    void _constructor() native "Vertices_constructor";
  
negative.code:   /// given recorder.
    Canvas(PictureRecorder recorder, Rect cullRect) {
      if (recorder == null)
        throw new ArgumentError('"recorder" must not be null.');
      if (recorder.isRecording)
        throw new ArgumentError('"recorder" must not already be associated with another Canvas.');
      if (!cullRect.isFinite)
        throw new ArgumentError('"cullRect" must not contain infinite or NaN coordinates.');
      // TODO(ianh): throw if recorder is defunct (https://github.com/flutter/flutter/issues/2531)
      _constructor(recorder, cullRect.left, cullRect.top, cullRect.right, cullRect.bottom);
    }
  