Make MediaWriter stop and pause return errors if necessary

o Make the API consistent with SF framework, which the MediaSource
  provides a return status for stop

o Also, helps to convey errors that occurred right when a
  premature stop() is called, leading to a potentially
  mal-formed output file.

Change-Id: I52a932345f38570fdf8ea04d67d73dd94ccd30ef
8 files changed