Enable by default in Chrome Secure Shell

[ralimi]

From a review left on the Chrome Webstore: "would be great to be able to activate by default the ssh-agent option in the chrome shell."

[ralimi]

@vapier - do you have thoughts on this?

[vapier]

we automatically probe for Google corp extensions, so probing for this one too shouldn't be a problem.

make sure the extension has a "hello" type message we can send it to see if it's alive. then fell free to send us a CL.

[vapier]

as a follow up to that, maybe you would consider merging this functionality into secure shell directly?

[ralimi]

Thanks @vapier! I'll look into probing for this one as well.

It is appealing to looking into merging in the long run. I'd be interested to see how best to accomplish that, but outside the context of this bug. Filed #41 for that.