The Global Media Controls use information from the Media Session service as well as other sources (e.g. Cast sessions) to provide a set of controls for all currently active media items, so it is layered on top of the Media Session service instead of being a part of it. This component provides UI to its users in the form of Views components.
This component is or will be used by both //chrome and //ash, so it cannot directly depend on either or on //content (since //ash cannot depend on //content).