The latest Google Chrome Beta version includes Web MIDI support for Android, Windows, Mac, Linux and Chrome OS. So good news for Chromebook users!
from the chromium blog:
Connecting to MIDI devices from the web
MIDI is a well-established communication protocol used by music devices such as synthesizers, DJ decks, and drum machines. In Chrome 43, users are able to use MIDI hardware to create music without installing any specialized software, as the Web MIDI API allows websites to communicate with connected MIDI devices such as a USB-MIDI drum machine plugged into an Android tablet.