MTP: Add support for syncing MTP playlists

MTP playlists now correspond to playlists in the media provider
(like those created by the Music app).

Change-Id: I085cb3cff003037ad62f0e297fb0cfd3047cb3a2
Signed-off-by: Mike Lockwood <lockwood@android.com>

core/java/android/provider/MediaStore.java

@@ -273,6 +273,13 @@ public final class MediaStore {
                     + "/object/" + objectId);
         }
 
+        // used for MTP GetObjectReferences and SetObjectReferences
+        public static final Uri getReferencesUri(String volumeName,
+                long objectId) {
+            return Uri.parse(CONTENT_AUTHORITY_SLASH + volumeName
+                    + "/object/" + objectId + "/references");
+        }
+
         /**
          * Fields for master table for all media files.
          * Table also contains MediaColumns._ID, DATA, SIZE and DATE_MODIFIED.