Whenever flutter master changes or you update flutter it has to download a variety of support packages. e.g.:

Downloading android-x86 tools...                      2.6s
Downloading android-x64 tools...                      2.8s

I'm not sure how frequently these packages are changing. If they don't change frequently, it would be good to cache these so that you don't have to wait for them to download each time you want to rebuild the flutter tool.