public static CustomTabsSession.PendingSession newPendingSession(
            Context context, final CustomTabsCallback callback, int id) {
        PendingIntent sessionId = createSessionId(context, id);

        return new CustomTabsSession.PendingSession(callback, sessionId);
    }
Creates a new pending session with an optional callback. This session can be converted to
a standard session using {@link #attachSession} after connection.

{@see PendingSession}
customtabs/src/android/support/customtabs/CustomTabsClient.java