Why not allow based on DNS, then you don't need to keep track of all the IPs...
Here's our whitelist...
`
^(.*\.)?gmail\.com$
^(.*\.)?gmailblog\.blogspot\.com$
^(.*\.)?google\.com$
^(.*\.)?googleapis\.com$
^(.*\.)?googleblog\.blogspot\.com$
^(.*\.)?googledrive\.com$
^(.*\.)?googleenterprise\.blogspot\.com$
^(.*\.)?googleonlinesecurity\.blogspot\.com$
^(.*\.)?google-opensource\.blogspot\.com$
^(.*\.)?googlevoiceblog\.blogspot\.com$
^(.*\.)?googleusercontent\.com$
^(.*\.)?google-analytics\.com$
^(.*\.)?googlecode\.com$
^goo\.gl$
`