The (KEYED_)LOAD/STORE_ICs didn't properly leave the UNINITIALIZED as
long as the receiver was always null/undefined. This leads to
deoptimization loops in TurboFan, because the compiler always put in a
SOFT deoptimization at this point.

Bug: v8:6989
Change-Id: I1a32bfb722f121f8b593e8972e657290d7b0531d
Reviewed-on: https://chromium-review.googlesource.com/735319Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48854}