Remote control displays expose an IRemoteControlDisplay interface
which they register through AudioManager.
Remote control clients create a RemoteControlClient object, which
implicitely exposes an IRemoteControlClient interface registered
in AudioService through AudioManager.
AudioService tells all clients and displays when a new client
is the one that should be displayed.
A client's data gets sent to the display when it is valid, or
it sets new data (while being valid).
The implementation for setting metadata and album art is temporary,
and will migrate to the MetadataEditor API in future CLs.
Change-Id: Ibab6ea1d94c68f32482c760c6ae269541f885548
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