This CL adds the bare minimum of source map generation for the kernel
pipeline in DDC.
It additionally introduces a testing framework that compiles dart files
with DDC (with or without kernel), steps through it via D8 and compares
the positions stopped at to the expected stop positions.
Bug:
Change-Id: Ie9e06164d8e51c973b83c46a8472e044876e4317
Reviewed-on: https://dart-review.googlesource.com/20662
Reviewed-by: Vijay Menon <vsm@google.com>
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Commit-Queue: Jens Johansen <jensj@google.com>