chrome-extension:

chrome-extension: URL scheme

[1] url_constants.cc - chrome/common - Code Search ( (2011-02-11 16:29:55 +09:00 版)) <http://www.google.co.jp/codesearch/p?hl=ja#hfE6470xZHk/chrome/common/url_constants.cc&q=package:chromium>

[2] Overview - Google Chrome Extensions - Google Code ( (2011-07-04 22:40:04 +09:00 版)) <http://code.google.com/chrome/extensions/overview.html>

[3] Overview - Google Chrome (2016-12-12 11:45:27 +09:00) <https://developer.chrome.com/extensions/overview>

As you might notice while you use the Google Chrome debugger, every file in an extension is also accessible by an absolute URL like this:
chrome-extension://<extensionID>/<pathToFile>
In that URL, the <extensionID> is a unique identifier that the extension system generates for each extension. You can see the IDs for all your loaded extensions by going to the URL chrome://extensions. The <pathToFile> is the location of the file under the extension's top folder; it's the same as the relative URL.