chromium-browser --headless --disable-gpu --print-to-pdf=output_file_name.pdf file:///path/to/your/html
Capturing the PDF at even the onload event (let alone the useless DOMContentLoaded event) is going to capture an incomplete picture in a huge number of situations. Frankly, a PDF capture at onload event is going to be utterly unusable. Is there a way to set a delay before capturing, ie: 10 seconds?
In an ideal world, a true "finished loading" event would trigger only after all DOMContentLoaded and onload handlers are executed, only once any AJAX requests launched by such handlers are completed (including requests fired off in their handlers, recursively). Of course, websockets and long polling ajax would still interfere with detecting a true "finished" event, but it'd be better than setting an artificially large delay of 10+ seconds.
Except then it was just a case of "wait 30 seconds and pray" because there was none of this fanciness.
(bloody kids, get off my lawn, banging two rocks together, etc.)
It works very well, but there are some gotchas with regard to the Chrome Remoting Interface.