ashmem: ensure ashmem fds are CLOEXEC.

Fix the memfd_create(2) path and add the missing unit test.

Bug: https://issuetracker.google.com/165667331
Test: treehugger
Change-Id: Ibb5c1d0f9d7caba1df04d1f03e82e55026d9f86a
2 files changed