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Use the utility method IMediaDeathNotifier::getMediaPlayerService()
to get a reference to media player service.  It retries after errors,
and keeps a single global per-process reference to the service rather
than one per object.  If we still can't contact the media player service
after retries, handle it like an unsuccessful prepare.

Miscellaneous:
 - Remove unused field Parcel metadatafilter

Change-Id: I451a64bd76b4a7f157774abe967448ec081f1014