Add TEST_MAPPING for DownloadProvider. am: 067c09636f am: a8486a85c8 am: 8c11961c83 am: 19fce42a0e

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

Change-Id: I8e0f027e8751f67ba2ffcaf1b9faa03bb555ae79