Part of https://chromium-review.googlesource.com/1231994 that landed
earlier, but was reverted due to breakage. Landing this cleanup
separately instead.

Drive-by-fix: Also add test coverage for the cases that weren't covered
properly (according to the test coverage bot).

Bug: chromium:225811, v8:8015
Change-Id: I9c13ed5fcf0ba9e6b190489e15df86970eafdc13
Reviewed-on: https://chromium-review.googlesource.com/1236213Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56087}