Add TEST_MAPPING for DownloadProvider. am: 067c09636f am: a8486a85c8

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

Change-Id: I2889c68949e82bfbf3a52a4d22a99e4f1fcfeba3