b36633357c
Instead of extending the TreeVisitor which provides an incorrect implementation of all methods, merely implement the TreeVisitor to require an implementation in CloneVisitor. Change-Id: Ied7d3b8062ee380e766c737e844a24b0b746312d Reviewed-on: https://dart-review.googlesource.com/41926 Reviewed-by: Dmitry Stefantsov <dmitryas@google.com> Commit-Queue: Kevin Millikin <kmillikin@google.com>