(I'm the Flutter TL.)

As far as the bit about Flutter goes: Flutter was started by engineers from the Chrome team, and myself (who worked in the open source team as editor of the HTML standard). We had no relationship with the Dart team at all until some times into the project, when we were looking around for a language to replace JavaScript in our project (codenamed Sky at the time). We considered a large number of languages but ended up picking Dart because it was the best fit (see the Flutter FAQ for more details). We then had to learn Dart and made friends with the Dart team, with whom we now work very closely.