public Bundle extraCommand(String commandName, Bundle args) {
        try {
            return mService.extraCommand(commandName, args);
        } catch (RemoteException e) {
            return null;
        }
    }
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