A DoS attack is typically easy to perform when the attacker has more computing and network resources than the victim. Being that you are using a typical consumer computer to talk to a collection of servers, the servers have both more computing power and more network resources than you. So it would be trivial for them to perform an attack. As you suggest, one way to achieve this would be simply overloading your network connection. Various timeouts and protections in place on your computer, your router, and the network of your ISP will provide some protection, but there really is no absolute protection against a foe as powerful as Google. If Google were determined, I suspect that they could take out your ISP's local infrastructure, performing a DoS on everyone in your region.
One interesting amplification DoS attack may be for Google's DNS servers to return your IP address for any request made to them (because of NAT, Google might have to return the IP address of your ISP). This would cause all of Google's DNS users to bombard your or your ISP's network. China came up with an similar attack using their so called Great Cannon. These attacks are hard to deal with because they cause innocent clients to partake in the attack, making filtering difficult.
The real prevention against these sorts of attacks is not technical (at least in the short term), but rather social and legal. Simply, this behavior would be bad for Google's business model. If they messed with their DNS server, people would stop using them. If this continued, ISPs would eventually start blocking all Google traffic and legal actions would be taken. One of the reasons that China's Great Cannon attack was so successful (it lasted weeks) is that it is supported by the government and there are no alternative ISPs. Something that is definitely not the case for Google.