Since 94ce16b7, when loading an iterator from null or undefined, we
generate the error message "x is not iterable" instead of the unwieldy
"Cannot read property 'Symbol(Symbol.iterator)' of undefined". However
Runtime::GetObjectProperty, which is used as slow path by LoadICs, did
not check for this case, leading to different messages being generated
depending on IC state.

Bug: chromium:823130
Change-Id: Ie98500b97efef401aac9880b9af47d58c3c2825d
Reviewed-on: https://chromium-review.googlesource.com/1042951Reviewed-by: Sathya Gunasekaran <gsathya@chromium.org>
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52974}