title: Dart's equivalent for Java's StringBuilder
body: <p>Is there a Dart equivalent for Java's <a href="https://docs.oracle.com/javase/7/docs/api/java/lang/StringBuilder.html" rel="noreferrer">StringBuilder</a>?</p>
  <p>I have looked into <a href="https://api.dartlang.org/1.14.2/dart-core/StringBuffer-class.html" rel="noreferrer">StringBuffer</a>, but that API doesn't have as many features as the StringBuilder. Methods like delete, reverse or variety for insert are missing in the StringBuffer.</p>
  <p>Follow-up - <a href="http://github.com/dart-lang/sdk/issues/25897" rel="noreferrer">request feature</a></p>