LengthAndHashOffset describes the value stored in the offset better.

Bug: v8:6404
Change-Id: Ie5ea2a362c54aa03e0a4e314d1adb8b91d74a044
Reviewed-on: https://chromium-review.googlesource.com/624458Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Sathya Gunasekaran <gsathya@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47503}