So far we generated source positions and safepoint information, but we
never actually attached it to the generated code objects. This CL adds
that.

R=titzer@chromium.org

Bug: v8:6600, chromium:793694
Change-Id: I8f4c6d8752f4c31a1df51c4893c262ea5925f3b5
Reviewed-on: https://chromium-review.googlesource.com/824266Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50077}