Loading html from qrc in QtWebEngine fails

Attempts to load html files from the qrc scheme fail. If you poke around in dev tools, you get this message upon setting window.location.href to a QRC URL pointing to an HTML file:
vm404:1 Resource interpreted as Document but transferred with MIME type application/x-extension-html

This ultimately seems to be the root cause of the issue: a wrong mimetype is detected for .html files in QRC. QMimeDatabase detects the file as application/x-extension-html rather than text/html, reports that to the QrcUrlSchemeHandler, which reports back to the QWebEngineUrlRequestJob, which eventually gets back to Chromium, which sees it got a non-text/html page, and decides it doesn't know what to do with it, rendering nothing.