I'm currently trying to work out how MIDI is supposed to work in Chromium on Linux. I'm on Gentoo. I've got Chromium 52.0.2743.60 installed. The midi access object obtained from navigator.requestMIDIAccess has an output map of length zero, so apparently chromium doesn't know of any MIDI outputs on my system.
I don't have any MIDI hardware connected. I fired up Qsynth and qjackctl and VMPK and managed to get sound from VMPK to my speakers, so I seem to have a working MIDI pipeline. I see the connection from VMPK to FLUID Synth in the qjackctl connections window, in the ALSA tab. But I don't see Chromium as a possible MIDI source there.
What do I have to do to connect chromium to my software synthesizer? Are there any manuals about this? I couldn't find any. Are there any steps along the path I could check to narrow the problem down?