ART: Add dex2oat swap usage test

Add a test that checks that native alloc size goes down when using
swap, as an indication that we're actually effectively using swap.

Bug: 29259363
Test: m test-art-host-gtest-dex2oat_test
Change-Id: Ifa5aef1b97696309283de78be08699a6399a4d1d
2 files changed