27976 Roll Dart SDK from 749ee4e9e053 to defd2ae02a3f (2 revisions) (cla: yes, waiting for tree to go green)

27978 Use runtime checks for arguments, out directory (cla: yes, waiting for tree to go green, needs tests)

27981 Roll Dart SDK from defd2ae02a3f to 2ca55ab863e9 (1 revision) (cla: yes, waiting for tree to go green)

27982 Roll Fuchsia Mac SDK from CYrOc5v2a… to 65ocmUBj5… (cla: yes, waiting for tree to go green)

27983 Roll Dart SDK from 2ca55ab863e9 to 0e1f5a68c69f (1 revision) (cla: yes, waiting for tree to go green)