Google Contacts sync - field mapping

[ieu]

We would like to fill some fields in Google with content from a contact in Espo.
Can you point me to where this is done? We have the Advanced Pack and are using a special implementation for companies (1:m). Hence, the company name is not synched to Google.
So I mostly need to know where in the code I can find the part where the fields are mapped.

Thanks in advance