Update android.media.AudioTrack.getTimestamp API documentation

   /**

    * Poll for a timestamp on demand.

    *

    * Use if you need to get the most recent timestamp outside of the event callback handler.

    * Calling this method too often may be inefficient;

    * if you need a high-resolution mapping between frame position and presentation time,

    * <p>

    * If you need to track timestamps during initial warmup or after a routing or mode change,

    * you should request a new timestamp once per second until the reported timestamps

    * show that the audio clock is stable.

    * Thereafter, query for a new timestamp approximately once every 10 seconds to once per minute.

    * Calling this method more often is inefficient.

    * It is also counter-productive to call this method more often than recommended,

    * because the short-term differences between successive timestamp reports are not meaningful.

    * If you need a high-resolution mapping between frame position and presentation time,

    * consider implementing that at application level, based on low-resolution timestamps.

    * <p>

    * The audio data at the returned position may either already have been

    * presented, or may have not yet been presented but is committed to be presented.

    * It is not possible to request the time corresponding to a particular position,

    *         be presented.

    *         In the case that no timestamp is available, any supplied instance is left unaltered.

    */

    // Add this text when the "on new timestamp" API is added:

    //   Use if you need to get the most recent timestamp outside of the event callback handler.

    public boolean getTimestamp(AudioTimestamp timestamp)

    {

        if (timestamp == null) {