Instead of storing {start} and {error_pc} we now store the
{error_offset}, which is anyways the only value we use.

R=clemensh@chromium.org

Change-Id: Ifd9791eff5c9efce2e7e2a1989bf3b5eaa464a02
Reviewed-on: https://chromium-review.googlesource.com/471527
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44510}