This is preparation for supporting OOB loads from strings, which
requires the KeyedLoadIC to track this information.

Bug: v8:6936, v8:7014
Change-Id: Ide132244ee523397dd418d21fe3377976f6633fd
Reviewed-on: https://chromium-review.googlesource.com/743481Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49026}