In my case, with GitHub Desktop for Windows (as of June 2, 2016) & Android Studio 2.1:
This folder ->
C:\Users\(UserName)\AppData\Local\GitHub\PortableGit_<hash>\
Contained a BATCH file called something like 'post-install.bat'. Run this file to create a folder 'cmd' with 'git.exe' inside.
This path-->
C:\Users\(UserName)\AppData\Local\GitHub\PortableGit_<hash>\cmd\git.exe
would be the location of 'git.exe' after running the post-install script.