This patch reduces the cost of the predicate that computes whether an
object contains only data or may contain pointers.

This also guards pushing to the copy_list_ with the predicate.

Bug: chromium:852420
Change-Id: I55c4e15eb8341708a21f484fb95b2c2cc2b25143
Reviewed-on: https://chromium-review.googlesource.com/c/1430068
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59074}