There are many changes:
* this text was added: "Google has a zero-tolerance policy against child sexual abuse imagery. If we become aware of such content, we will report it to the appropriate authorities and may take disciplinary action, including termination, against the Google Accounts of those involved."
* this text was added: "You can report abuse by using this form. Google may disable accounts that are found to be in violation of these policies. If your account is disabled, and you believe it was a mistake, please follow the instructions on this page."
* this text was removed: "Google may terminate your account in accordance with the terms of service if you fail to login to your account for a period of nine months."
* this text was removed: "You must promptly notify Google of any breach of security related to the Services, including but not limited to unauthorized use of your password or account. To help ensure the security of your password or account, please sign out from your account at the end of each session."
* the list of prohibited actions no longer includes: "conduct or forward pyramid schemes and the like", "transmit content that may be harmful to minors", "impersonate another person", "use Gmail to violate the legal rights (such as rights of privacy and publicity) of others", "create multiple user accounts in connection with any violation of the Agreement or create user accounts by automated means or under false or fraudulent pretenses", "sell, trade, resell or otherwise exploit for any unauthorized commercial purpose or transfer any Gmail account", "modify, adapt, translate, or reverse engineer any portion of the Gmail Service", "remove any copyright, trademark or other proprietary rights notices contained in or on the Gmail Service", "reformat or frame any portion of the web pages that are part of the Gmail Service", "use the Gmail Service in connection with illegal peer-to-peer file sharing".
The policies about child sexual abuse imagery have already been added to Picasa Web Albums back in 2008 and Google actually used them last year. "The FBI says the investigation began in March when Google's hashing technology found two child porn pictures in his Picasa library. Picasa is a cloud-sharing platform for images owned by Google."
"Since 2008, we've used 'hashing' technology to tag known child sexual abuse images, allowing us to identify duplicate images which may exist elsewhere. Each offending image in effect gets a unique ID that our computers can recognize without humans having to view them again," informs a Google blog post from 2013.
So it seems like an existing Picasa Web Albums policy was added to Gmail and other Google services: Play Store, Build with Chrome, Blogger, Google Drive and probably other services. Google has also "fine-tuned Google Search to prevent links to child sexual abuse material from appearing in search results."