To repro:

1. Launch an Electron app (hello world/default fiddle will do)
2. Open DevTools
3. Find a minified JS file, e.g. renderer_init.js
4. Click the "Pretty Print" button in DevTools

Expected behavior:
The JS in the DevTools view is replaced with a pretty-printed version of the code

Actual behavior:
The JS in the DevTools view is unchanged


Bisected to https://github.com/electron/electron/compare/v11.0.0-nightly.20200721...v11.0.0-nightly.20200723
shell/browser/ui/devtools_ui.cc
return GURL(std::string("devtools://devtools/") + path).path().substr(1);
}
std::string GetMimeTypeForPath(const std::string& path) {
  std::string filename = PathWithoutParams(path);
  if (base::EndsWith(filename, ".html", base::CompareCase::INSENSITIVE_ASCII)) {
    return "text/html";
  } else if (base::EndsWith(filename, ".css",
                            base::CompareCase::INSENSITIVE_ASCII)) {
    return "text/css";
  } else if (base::EndsWith(filename, ".js",
                            base::CompareCase::INSENSITIVE_ASCII)) {
    return "application/javascript";
  } else if (base::EndsWith(filename, ".png",
                            base::CompareCase::INSENSITIVE_ASCII)) {
    return "image/png";
  } else if (base::EndsWith(filename, ".gif",
                            base::CompareCase::INSENSITIVE_ASCII)) {
    return "image/gif";
  } else if (base::EndsWith(filename, ".svg",
                            base::CompareCase::INSENSITIVE_ASCII)) {
    return "image/svg+xml";
  } else if (base::EndsWith(filename, ".manifest",
                            base::CompareCase::INSENSITIVE_ASCII)) {
    return "text/cache-manifest";
  }
  return "text/html";
}
class BundledDataSource : public content::URLDataSource {