The implementation of AndroidProtocolHandler for the special file://android_asset/ and file://android_res/ URLs implements getMimeType just by passing the file extension to java.net.URLConnection.guessContentTypeFromName.

This means that it won't necessarily guess the same MIME types as normal file: URLs, which use Chromium's internal MIME type map instead of Android's.

We should probably see if there's a way to use Chromium's instead, since Android's map may not include all file types that Chromium can actually render.