Is anyone still interested in this? I am considering writing an AVRDude-like program in pure HTML5/Javascript for starters so a Chromebook can load on hex files to an Arduino. Although this is not the complete package, it's a big hurdle apparently.
I have written ChromeOS USB serial applications before (actually, it works in any chrome browser incidentally). I assume that the Atmel App Note AVR068 "STK500 Communication Protocol" is what the Arduino serial port loader uses? Is there any other documentation out there?
While I have done extensive development on the Arduino platform from an end user and library perspective, I have not dove this deep into the bootloader.