In an out-of-the-way Google office, two life-size humanoid robots hang suspended in a corner. If Amazon can imagine delivering books by drones, is it too much to think that Google might be planning to one day have one of the robots hop off an automated Google Car and race to your doorstep to deliver a package? Google executives acknowledge that robotic vision is a “moonshot.” But it appears to be more realistic than Amazon’s proposed drone delivery service, which Jeff Bezos, Amazon’s chief executive, revealed in a television interview the evening before one of the biggest online shopping days of the year. Over the last half-year, Google has quietly acquired seven technology companies in an effort to create a new generation of robots. And the engineer heading the effort is Andy Rubin, the man who built Google’s Android software into the world’s dominant force in smartphones.