Includes various fixes and cleanups here and there.

Bug: v8:7703, v8:8852
Change-Id: I603eb0212cab3fecabfa15dceb70ee23b81cdb5a
Reviewed-on: https://chromium-review.googlesource.com/c/1491595Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59909}