Content embedders should be unique services, rather than merging API surface with services provided by content. As a consequence, much of (all of?) content's various broker pipes should be considered private implementation details rather than being exposed via content/public.
See https://groups.google.com/a/chromium.org/d/msg/services-dev/WIBTutb40mk/syPVH-TJBAAJ for more detail.
Comment 1 by bugdroid1@chromium.org
, Aug 11 2017