We don't pull any resources from Google (or any of the other companies who contribute to Flutter, like Microsoft, Cannonical, Nevercode, etc) at runtime.

During development time we pull binaries from Google servers (for lack of a better place to put them mostly) and source from GitHub, and as Tim said there's some analytics (there's a big message saying how to opt of analytics when you first start the flutter command line tool).

I know the web site says Flutter is "made by Google" but that's really underselling how much Flutter is a group effort by lots of contributors, a (very active) minority of which happen to work for Google.

The whole project is open source, there's no closed-source component, and lots of people build their own binaries, for what it's worth. So you don't have to trust me on any of this. :-)