Except given the recent trend, too many decisions like that would likely result in LibreAlloy or something similar. They have a lot more breathing room to behave that way with gmail and Youtube and similar, where the value they are providing is in serving the content, as opposed to Chrome where the code is more or less available and their value is in developing the open source environment.

Clarification: I'm not sold on the "Upstream goes sour? Time to Libre$thing" trend as a good thing in the long term, but I doubt the potential for it to occur has escaped Google's notice.