(The test that catches the bug was test-bytecode-generator/LookupSlot)

BUG=v8:5516

Change-Id: I00a02c5326b2a132383a9d72b5b894fade53bbf2
Reviewed-on: https://chromium-review.googlesource.com/558864
Commit-Queue: Marja Hölttä <marja@chromium.org>
Reviewed-by: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46374}