Add TEST_MAPPING for DownloadProvider. am: 067c09636f am: a8486a85c8 am: d79fa86728 am: 56e5d3a06a

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/providers/DownloadProvider/+/11839720

Change-Id: I5653a244c675a0913e228b35aeeedf2bb3581b61