mobile/audio: player should close its audio source
mobile/audio: player should close its audio source

The most common use case to init a player is to open an asset and provide
it to NewPlayer. Currently, we require use to keep a reference to the source
and close it after the player is destroyed. It's tedious. We may improve
the usability by freeing the source asset on Destroy. And if the user
wants to play a ReadSeeker, they can implement a trivial ReadSeekCloser
with a noop Close.

Change-Id: Ie6bdea468da484f785bc0c283f13203cad3a1a68
Reviewed-on: https://go-review.googlesource.com/9693
Reviewed-by: Nigel Tao <58ae08b3356928ff9c67562b4719487d54fe8348@golang.org>

cainiaocome/mobile,b54898533/mobile,lonphy23t/mobile,goldcaddy77/mobile,0x90sled/mobile,qskycolor/mobile,xing/gomobile,steeve/mobile,cainiaocome/mobile,zach-klippenstein/mobile,qskycolor/mobile,freeman0211/mobile,xing/gomobile,zach-klippenstein/mobile,swisspol/mobile,MaxCy330/mobile,freeman0211/mobile,DanielWorld/mobile,xing/gomobile,swisspol/mobile,tempbottle/mobile,golang/mobile,ppamorim/mobile,swisspol/mobile,steeve/mobile,steeve/mobile,DanielWorld/mobile,swisspol/mobile,swisspol/mobile,tempbottle/mobile,freeman0211/mobile,tempbottle/mobile,samanalysis/mobile,0x90sled/mobile,samanalysis/mobile,ichu501/mobile,b54898533/mobile,goldcaddy77/mobile,samanalysis/mobile,b54898533/mobile,ppamorim/mobile,qskycolor/mobile,samanalysis/mobile,b54898533/mobile,goldcaddy77/mobile,0x90sled/mobile,ppamorim/mobile,cainiaocome/mobile,golang/mobile,b54898533/mobile,samanalysis/mobile,lonphy23t/mobile,MaxCy330/mobile,ichu501/mobile,goldcaddy77/mobile,zach-klippenstein/mobile,golang/mobile,xing/gomobile,ichu501/mobile,freeman0211/mobile,DanielWorld/mobile,MaxCy330/mobile,ichu501/mobile,steeve/mobile,zach-klippenstein/mobile,cainiaocome/mobile,MaxCy330/mobile,tempbottle/mobile,ppamorim/mobile,cainiaocome/mobile,ichu501/mobile,goldcaddy77/mobile,tempbottle/mobile,golang/mobile,ppamorim/mobile,0x90sled/mobile,0x90sled/mobile,MaxCy330/mobile,lonphy23t/mobile,lonphy23t/mobile,xing/gomobile,DanielWorld/mobile,lonphy23t/mobile,qskycolor/mobile