Minor cleanup moving some types to more meaningful headers.

Bug: v8:8015
Change-Id: I99e428529f0b2d967a3c67385c80001bb0df19fa
Reviewed-on: https://chromium-review.googlesource.com/1195506Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Stephan Herhut <herhut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55511}