28818 Roll Dart SDK from eba0c93d96de to 1d7f47bf04d8 (1 revision) (cla: yes, waiting for tree to go green)

28820 [fuchsia] Rename FuchsiaExternalViewEmbedder to GfxExternalViewEmbedder (cla: yes, platform-fuchsia)

28821 [Fuchsia] Notify Shell when memory becomes low. (cla: yes, waiting for tree to go green, platform-fuchsia, needs tests)

28823 [fuchsia] Small shell scripts for workflow. (cla: yes, waiting for tree to go green)

28825 Roll Fuchsia Mac SDK from c3_45l-Rd… to lD33hO1tW… (cla: yes, waiting for tree to go green)