This fix works for all versions of Windows. Windows 7, 8, 8.1, and 10.
Go to the actual folder in its C:\Users\<your name>\Google Drive\ (NOT the Google Drive folder listed under 'FAVOURITES' which is a shortcut).
Right click 'Google Drive' > Security tab > Advanced > Click your username (mine showed <not inherited>) > Click 'Change Permissions' > Check the 'Include inheritable permissions...' box > Click ok.
Search indexing of Google Drive should then begin in the background.
After changing these settings in an offending Windows 7 computer, indexing happened almost immediately.