This is the first of a series of refactoring CLs to make way for
Windows trap handling support.

See https://chromium-review.googlesource.com/c/v8/v8/+/626558 as well.

Bug: 
Change-Id: I5fe9ef9c1cec58a81e51fcffbbe4419e0e298ab7
Reviewed-on: https://chromium-review.googlesource.com/644104Reviewed-by: Brad Nelson <bradnelson@chromium.org>
Commit-Queue: Eric Holk <eholk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48191}