This moves the logic previously used in DDC for testing stepping via
sourcemaps to a shared location so both DDC and dart2js can make use
of the same thing.
Bug:
Change-Id: I83a2b1fc4fe5cefe3c8537e50d03c3e41e0490a8
Reviewed-on: https://dart-review.googlesource.com/24110
Commit-Queue: Jens Johansen <jensj@google.com>
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Jens Johansen