Think about what you're saying, you're saying Google is going to sit there and review all of the source code, and all patches and new releases to that source code. Really? Do you actually believe this...
As per China having the source, do you really think it matters? If someone wants to break in, they're going to get in... (regardless if its Windows/Linux/Mac) why... because that's their job and they are going to spend every minute of every day until they figure it out, and that's what makes them better than you. Majority of the time the issue is not software itself, but the policies in place. Hell, why even break in technically, when I can probably call one of these 10,000 employees up and they'll give me their password. Duh.
If you believe security is 1-dimensional, then you are bound to fail. History has shown this time and time again, just read a book / biography in regards to this topic.