The baseline compiler needs to know the depth in order to access the
parent block. This is a small CL, but anything that can land before the
big baseline CL reduced the complexity of the latter.

R=ahaas@chromium.org

Bug: v8:6600
Change-Id: I2e29cc974908438266adb4301026dfe5fbfb1990
Reviewed-on: https://chromium-review.googlesource.com/677301Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48112}