29056 add heartbeat (cla: yes)

29057 Fix Flex class docs by replacing ‘vertical space’ with ‘space on its main axis’ so that the language fits both column and row. (cla: yes, framework, waiting for tree to go green)

29062 fix windows codegen (cla: yes, tool)

29064 Revert “Lazily download artifacts (III)” (cla: yes)

29069 Heroes and nested Navigators (a: animation, cla: yes, framework)

29072 Update to ListView Sample Code in API Docs (cla: yes, d: api docs, d: examples, framework)

29073 Make sure test reporter prints out stderr, and disables Bigquery for non-contributors (a: tests, cla: yes, team)