I've made a tool to easily search into the most recent Apps and Extensions APIs. It is still a beta version, but I would appreciate your feedback.
Please, check it at http://chrome-api.storage.googleapis.com/site/search.html
It should be self-explanatory. You can click on namespaces and methods to get detailed descriptions. It is updated daily with the latest APIs from Chromium trunk.
Please, let me know if you find it useful, and fill bugs in the Github project as you find them :-)