Dartdoc > 0.18.1 allows generation of source code links
to documented objects. Enable this for the Dart SDK build.
Change-Id: Ib385d3e51f6f5852f37e591d7a60ba7b4e7f93c1
Reviewed-on: https://dart-review.googlesource.com/c/92303
Reviewed-by: Alexander Thomas <athom@google.com>
Commit-Queue: Janice Collins <jcollins@google.com>
Janice Collins