Change manifest version to 2.
Use chrome.extension instead of chrome.self which is removed.
Use sendMessage and onMessage instead of sendRequest and onRequest.
Change popup to default_popup in browser_action.
Create external JavaScript files, because inline JavaScripts will not be
executed in the new Content Security Policy.
Merge pull request #3 from hnakamur/migrate_to_manifest_v2

Migrate to manifest v2