I believe you will find that as of just recently the _only_ way** to get an extension to run is if it is listed in the Chrome Web Store.
This is a policy which has been coming for awhile, and has arrived in increasing force.
Even if you want to develop for purely local/personal usage, it needs to go through the Web Store.
**Currently you can get around this by using the dev-m branch of the Chromium browser, but that is being listed as a temporary measure.
**Also, in the interests of full disclosure, you can get around this limitation by joining your machine to an AD network and pushing a GPO of allowed un-authorized extensions. But the process is tedious at best.