So far as I know, Gmail doesn't have a button to show you just your unread emails. I receive a lot of mail and I'm tired of writing in the search box "in:unread in:inbox".
So today I wrote a quick Chrome extension that injects an unread email button into Gmail. Could I have found an extension somewhere that does this? Probably, but I like to know what code is interacting with my emails. You can review the very short source code for this extension by downloading it below and reading the "run.js" file.