43471 flip track widget creation on by default (cla: yes, tool, waiting for tree to go green)

43479 Refactor gradle.dart (cla: yes, tool)

43511 Improve DropdownButton assert message (cla: yes, f: material design, framework)

43526 Change PopupMenuButton.icon type to Widget (cla: yes, f: material design, framework)

43528 Adjust and refactor all MaterialButton tests into its respective file (cla: yes, f: material design, framework, waiting for tree to go green)

43529 Cupertino web tests (cla: yes, f: material design, framework, team)

43544 Catch AppConnectionException (cla: yes, tool)

43546 Alias upgrade-packages => update-packages (cla: yes, tool)