First CL moving parsing output to a separate class.
Following CLs will move (and deduplicate) code from
testcases by sharing common features like comparing
stdout to the expected output.

Bug: v8:6917
Change-Id: I1174a985949a0b946cefbf7e7c91e8815cbb4f15
Reviewed-on: https://chromium-review.googlesource.com/834130
Commit-Queue: Michał Majewski <majeski@google.com>
Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50228}