[1] url_constants.cc - chrome/common - Code Search ( ( 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 ( ( 版)) <http://code.google.com/chrome/extensions/overview.html>
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.