This is an awful kludge:
To do this, create a script that traps all browser shortcuts and discards them. Save it as a Greasemonkey user script (name it
something.user.js) and set it to execute on all pages. You can use Chromium's built-in Greasemonkey support, or use any of various extensions if you prefer a different interface. The end result is that whenever you're on any web page (i.e. always), the script will have executed, causing most browser shortcuts to be trapped and discarded before the browser processes them.
Of course, you can write your script to not trap a particular shortcut that you actually use.
Note that there are a few shortcuts (generally related to navigating between tabs) that by design web pages are not allowed to trap. Those will therefore not be disabled.