origin:
https://chromium-review.googlesource.com/c/crosvm/crosvm/+/3944711
PageHandler handles events from userfaultfd using SwapFile.
tests are placed as integration tests since they rely on userfaultfd(2).
design document: go/tanooki-phase1-dd
BUG=b:215093219
TEST=cargo test -p swap page_handler
Change-Id: I64d213d27174d75ee618c4675ea52dbac58bfe59
Reviewed-on: https://chromium-review.googlesource.com/c/crosvm/crosvm/+/4016144
Reviewed-by: David Stevens <stevensd@chromium.org>
Commit-Queue: Shin Kawamura <kawasin@google.com>
