To run:
On host:
fx set <product>.<board> --with examples/fidl/dart:all fx build fx run fuchsia-pkg://fuchsia.com/example-launcher-dart#meta/example-launcher-dart.cmx fuchsia-pkg://fuchsia.com/echo-dart-client#meta/echo-dart-client.cmx fuchsia-pkg://fuchsia.com/echo-dart-server#meta/echo-dart-server.cmx fuchsia.examples.Echo