I've come across this before. I don't know what its full responsibilities are, but I know it's part of the Chrome update process.
I came across it when I was trying to get two totally separate Chrome installs working on one machine (using https://github.com/djbclark/chrome-schismator), in such a way that they can run in parallel, update in parallel, each totally isolated from one another. It seems as though it's not possible to have two Chrome installs update themselves separately due to the Keystone application only being able to store one reference to a Chrome install at a time, meaning that the other Chrome instance never detects that it's out of date.
I came across it when I was trying to get two totally separate Chrome installs working on one machine (using https://github.com/djbclark/chrome-schismator), in such a way that they can run in parallel, update in parallel, each totally isolated from one another. It seems as though it's not possible to have two Chrome installs update themselves separately due to the Keystone application only being able to store one reference to a Chrome install at a time, meaning that the other Chrome instance never detects that it's out of date.