Used this howto: https://support.google.com/chromeos/answer/2382577?hl=en

Works with my Chromebook, Windows 7 and Android (Samsung Galaxy SII)

Sometimes the Chromebook takes a little while to connect. And if it disconnects you may need to wait a few minutes before it will happily connect again.

The reason you have to go to these lengths is:

- Java doesn't install on a Chromebook (as far as I'm aware) so you can't use the ASA's clientless SSL VPN

- PPTP isn't an option on the Chromebook so you can't connect to a Microsoft PPTP server

To get Microsoft Remote Desktop (mstsc) functionality I have installed the "2X Client for RDP/Remote Desktop" on the Chromebook. So with it and the L2TP/IPSec VPN I have  connectivity back to my work network finally.