75895 Refactor Hero example (cla: yes, framework, waiting for tree to go green)

75899 Adding checkbox demo (cla: yes, f: material design, framework)

75903 deprecated consistency (cla: yes, f: material design, framework, team, waiting for tree to go green)

75920 Mark mac_android_smoke_catalina_start_up test as unflaky (cla: yes, team, waiting for tree to go green)

75922 [flutter_tools] use temp dir for tester dill, use desktop log reader (cla: yes, tool)

75925 [flutter_tools] add package:http to forbidden imports test (cla: yes, tool, waiting for tree to go green)

75927 [flutter_tools] Send flutter_immediately_exit_test to the elemental plane to be reforged anew (cla: yes, tool)