Add TEST_MAPPING for DownloadProvider. am: 067c09636f am: 4c592d410a am: cc287c9fee am: 83cf741149 am: 67f484d06f

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

Change-Id: I011bcf57afb88ddd9b84a719f90098855fceb412