Google Engineers mostly use their beefy workstations with a Google-flavored Ubuntu installed to code. Most engineers have Mac laptops though (at least my team), even though their use is quite limited (you cannot store code there, so mostly you have to ssh or remote desktop to your workstation)
That is generally true, but not completely so. A number of android engineers develop directly on Mac, and all iOS app developers do so because there isn't an alternative. And there are some weird engineers like me who mount their linux disks on their macs via nfs and only use their linux boxes to do command line work (builds, running servers, etc.).
Edit: for the apparent doubter of this, see any number of articles about Google's 40,000 macs that they use as dev machines, for example: https://www.usenix.org/conference/lisa13/managing-macs-googl... http://www.theregister.co.uk/2013/11/27/google_mac_support/