I think I'll just stick with pressing alt-tab to Terminal.app.

Another vote for Chrome Secure Shell. Open source, well made and hterm supports copying to your clipboard when tmux or mosh doesn't eat the sequence. I have limited font choice on the Chromebook so I embed a powerline font in mine. Very cool. Hacking up some insecure DIY server backend is a bit silly when you can have libssh or mosh compiled into nacl.

hterm -- the terminal implementation that the Chrome ssh plugin and crosh is based on is pretty hackable, too.

why would anyone use chrome ssh plugin instead of mate-terminal?

I don't get it.