Everything can be possible but I think that the owners of google have no need to mine. They have mountains of money and don't know what to do with those. They have already even a world class business which is the first ranked in its field. At the end I cannot believe that they can do something that can make bad to bitcoin and to its community. Have no reasons to do this. The power they will gain if will mine bitcoin (if decide to mine with this kind of computer) will give them nothing that them have not already. Or that cannot buy already. So, I don't see any threat of the Google computer for bitcoin.