getHeightOfCanvas function
Implementation
double getHeightOfCanvas(
    Matrix matrix, double defaultCellHeight, EdgeInsets cellPadding) {
  double height = 0.0;
  for (int y = 0; y < matrix.height(); y++) {
    height += (getHighestHeightInARow(matrix, defaultCellHeight, y) +
        cellPadding.top +
        cellPadding.bottom);
  }
  return height;
}