Add logging for MTP roots.

    private static final String AUTHORITY_MEDIA = "com.android.providers.media.documents";

    private static final String AUTHORITY_STORAGE = "com.android.externalstorage.documents";

    private static final String AUTHORITY_DOWNLOADS = "com.android.providers.downloads.documents";

    private static final String AUTHORITY_MTP = "com.android.mtp.documents";

    // These strings have to be whitelisted in tron. Do not change them.

    private static final String COUNT_LAUNCH_ACTION = "docsui_launch_action";

    // root that is not explicitly recognized by the Metrics code (see {@link

    // #getSanitizedRootIndex}). Apps are also bucketed in this histogram using negative indices

    // (see below).

    // Do not change or rearrange these values, that will break historical data. Only add to the end

    // of the list.

    private static final int ROOT_NONE = 0;

    private static final int ROOT_OTHER = 1;

    private static final int ROOT_AUDIO = 2;

    private static final int ROOT_IMAGES = 6;

    private static final int ROOT_RECENTS = 7;

    private static final int ROOT_VIDEOS = 8;

    private static final int ROOT_MTP = 9;

    // Apps aren't really "roots", but they are treated as such in the roots fragment UI and so they

    // are logged analogously to roots. Use negative numbers to identify apps.

    private static final int ROOT_THIRD_PARTY_APP = -1;

            ROOT_IMAGES,

            ROOT_RECENTS,

            ROOT_VIDEOS,

            ROOT_MTP,

            ROOT_THIRD_PARTY_APP

    })

    @Retention(RetentionPolicy.SOURCE)

                }

            case AUTHORITY_DOWNLOADS:

                return ROOT_DOWNLOADS;

            case AUTHORITY_MTP:

                return ROOT_MTP;

            default:

                return ROOT_OTHER;

        }