SourceSpanBase constructor

SourceSpanBase(SourceLocation start, SourceLocation end, String text)

Implementation 

SourceSpanBase(this.start, this.end, this.text) {
  if (end.sourceUrl != start.sourceUrl) {
    throw new ArgumentError("Source URLs \"${start.sourceUrl}\" and "
        " \"${end.sourceUrl}\" don't match.");
  } else if (end.offset < start.offset) {
    throw new ArgumentError('End $end must come after start $start.');
  } else if (text.length != start.distance(end)) {
    throw new ArgumentError('Text "$text" must be ${start.distance(end)} '
        'characters long.');
  }
}