The service handles three different types of `Intents`. Custom command and media
command Intents created by the library and media button event Intents from other
sources.
Media commands from the library as well as from external sources have the action
set to `android.intent.action.MEDIA_BUTTON`. If the data URI is set and can be
used to identify a session then it is a library Intent. If the Intent is coming
from an external KeyEvent, the service implementation is asked which session to use
by calling `onGetSession(controllerInfo)` with the controller info being an
anonymous legacy controller info.
Intents representing a custom command are always coming from the library and hence
always have a data URI.
Issue: androidx/media#82
PiperOrigin-RevId: 453932972
(cherry picked from commit 8b592fc77aeead345adac999eda27da55df0ae01)
7c0b787bdb