This is a reland of 3d023952
Original change's description:
> [runtime] Make JSFunction::prototype_or_initial_map field optional.
> 
> Functions that don't have prototype need to store neither prototype nor
> initial map, so the |prototype_or_initial_map| field is not required for
> such maps.
> 
> Bug: v8:6459
> Change-Id: I4b3066bd6a4fed42c19f217bae82a8bce552bdca
> Reviewed-on: https://chromium-review.googlesource.com/570250
> Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
> Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
> Commit-Queue: Igor Sheludko <ishell@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#46840}

Bug: v8:6459
Change-Id: I54e3516ea70474c6d4f873f7b91e74cb8a7d622a
Reviewed-on: https://chromium-review.googlesource.com/583307Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Benedikt Meurer <bmeurer@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48523}