Enable dragon drop for touch.

- Start a drag when the user long-presses on an already-selected item.
- Start a drag when the user mouse-drags on an already-selected item.
- Add highlighting of drop targets.

BUG=20556237

Change-Id: I450fd6768eeb08906304227385476942d641fd11
diff --git a/Android.mk b/Android.mk
index 1a4e3eb..e1650e1 100644
--- a/Android.mk
+++ b/Android.mk
@@ -8,6 +8,7 @@
 LOCAL_STATIC_JAVA_LIBRARIES := android-support-v4
 # The design lib requires that the client package use appcompat themes.
 LOCAL_STATIC_JAVA_LIBRARIES += android-support-v7-appcompat
+LOCAL_STATIC_JAVA_LIBRARIES += android-support-v13
 # Supplies material design components, e.g. Snackbar.
 LOCAL_STATIC_JAVA_LIBRARIES += android-support-design
 LOCAL_STATIC_JAVA_LIBRARIES += android-support-v7-recyclerview