Increase cache size and low-watermark threshold, also

MediaPlayer now sends out MEDIA_INFO,MEDIA_INFO_VIDEO_TRACK_LAGGING messages
to the JAVA client informing it how much (if at all) the video lags behind
audio (arg2 is the media delay in ms).

Change-Id: I6933f573d8597a35112e4b5ee0fcb826a7f6ddd1
related-to-bug: 3335220