Add RootTargetPreparer for explicitly specifying the root dependency am: 4cc54592

Original change: https://googleplex-android-review.googlesource.com/c/platform/frameworks/native/+/26804795



Change-Id: I93fc30977d946efe806b0e043a9e9e3b78b66847
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>