If you look at a list of Google acquisitions, the one that stuck out until today was GreenBorder, which was listed as "internal use" rather than being associated with a product or service. When Google picked up GreenBorder in May 2007, it was rather curious. Experts and analysts had some wild guesses about how GreenBorder might be used inside Google.
Few people seemed to foresee that Google would ship the technology inside a full-blown browser competitor to Internet Explorer and Firefox. Yet GreenBorder employees are definitely in the thick of Chrome's sandboxing work; the comic book's section on sandboxing names several former GreenBorder staff such as Mark Larson and Carlos Pizano.
The timing of Google Chrome's announcement is interesting because it comes just after IE8 has gone public with its feature set. Did Google pick this time to debut Chrome because it feels it already beats IE8? For example, IE8's InPrivate Browsing is functionally similar to Chrome's sandboxing, but doesn't appear to go nearly as deep architecturally. People won't be able to answer those questions until they can spend some time with Chrome.