Should be able to automatically merge all HTML, JS, CSS in one HTML file. Then you can save modified HTML page in a browser. This feature is good for bug reductions, but possibly is not so important for DOM Inspector general use.
Closing as invalid, as this bug pertains to the old inspector UI and/or its tests. Please file a new bug (https://www.webkit.org/new-inspector-bug) if the bug/feature/issue is still relevant to WebKit trunk.