This is just speculation, but I think it's possible somebody just did this in their free time without much strategic planning, like so many projects at Google (you know, that 20% free time at Google).
I have some idea of how easy it is to embed IE into apps, so I am going to assume it's at least the same order of easiness to embed Chrome into IE. I think it's fairly trivial, though perhaps unpleasant work.
I tried looking at the source code, but I don't use GIT so I gave up. It's part of Chromium: http://code.google.com/chromium/
EDIT: After considering your profile page I fold :)
Again, I don't think that this is a technical thing; but a corporate strategy thing. We didn't hear about this from some developer's blog; we heard about it from an "official" Google blog. At some point, this thing has been blessed for release under the Google umbrella.
