ashmem_test: Add tests related to memfd's size file seals Add tests to ensure that ashmem_valid() does not pass given a memfd without the right set of size file seals. Bug: 498720726 Cherrypick-From: https://googleplex-android-review.googlesource.com/q/commit:5ceaa348e48cb98a0e69c8771f1bd57b818484ba Merged-In: I1eff526094c2aa99d2e7a2645f77c8b5ec881905 Change-Id: I1eff526094c2aa99d2e7a2645f77c8b5ec881905