Fix comment about the coordinate system of the position.
Fix comment about the coordinate system of the position.

TEST=none
BUG=none
tonyjoule/ppapi,dralves/ppapi,huochetou999/ppapi,tonyjoule/ppapi,huochetou999/ppapi,JustRight/ppapi,huochetou999/ppapi,CharlesHuimin/ppapi,phisixersai/ppapi,dralves/ppapi,xinghaizhou/ppapi,stefanie924/ppapi,xuesongzhu/ppapi,HAfsari/ppapi,JustRight/ppapi,JustRight/ppapi,tiaolong/ppapi,fubaydullaev/ppapi,rise-worlds/ppapi,xuesongzhu/ppapi,tonyjoule/ppapi,dingdayong/ppapi,CharlesHuimin/ppapi,JustRight/ppapi,YachaoLiu/ppapi,Xelemsta/ppapi,Xelemsta/ppapi,CharlesHuimin/ppapi,gwobay/ppapi,whitewolfm/ppapi,xiaozihui/ppapi,HAfsari/ppapi,tiaolong/ppapi,siweilvxing/ppapi,chenfeng8742/ppapi,lag945/ppapi,dralves/ppapi,huqingyu/ppapi,dingdayong/ppapi,fubaydullaev/ppapi,thdtjsdn/ppapi,cacpssl/ppapi,CharlesHuimin/ppapi,ruder/ppapi,fubaydullaev/ppapi,xiaozihui/ppapi,phisixersai/ppapi,phisixersai/ppapi,thdtjsdn/ppapi,nanox/ppapi,huqingyu/ppapi,HAfsari/ppapi,chenfeng8742/ppapi,lag945/ppapi,nanox/ppapi,fubaydullaev/ppapi,JustRight/ppapi,chenfeng8742/ppapi,gwobay/ppapi,xiaozihui/ppapi,qwop/ppapi,phisixersai/ppapi,xinghaizhou/ppapi,ruder/ppapi,stefanie924/ppapi,whitewolfm/ppapi,cacpssl/ppapi,whitewolfm/ppapi,YachaoLiu/ppapi,stefanie924/ppapi,rise-worlds/ppapi,xinghaizhou/ppapi,Xelemsta/ppapi,xiaozihui/ppapi,tiaolong/ppapi,dingdayong/ppapi,huqingyu/ppapi,thdtjsdn/ppapi,c1soju96/ppapi,siweilvxing/ppapi,c1soju96/ppapi,cacpssl/ppapi,siweilvxing/ppapi,lag945/ppapi,xuesongzhu/ppapi,thdtjsdn/ppapi,dingdayong/ppapi,gwobay/ppapi,Xelemsta/ppapi,stefanie924/ppapi,dralves/ppapi,ruder/ppapi,cacpssl/ppapi,qwop/ppapi,lag945/ppapi,qwop/ppapi,tonyjoule/ppapi,HAfsari/ppapi,YachaoLiu/ppapi,xinghaizhou/ppapi,ruder/ppapi,chenfeng8742/ppapi,siweilvxing/ppapi,cacpssl/ppapi,c1soju96/ppapi,nanox/ppapi,qwop/ppapi,Xelemsta/ppapi,c1soju96/ppapi,YachaoLiu/ppapi,xiaozihui/ppapi,tonyjoule/ppapi,huqingyu/ppapi,tiaolong/ppapi,dralves/ppapi,nanox/ppapi,fubaydullaev/ppapi,c1soju96/ppapi,qwop/ppapi,xuesongzhu/ppapi,gwobay/ppapi,huochetou999/ppapi,ruder/ppapi,gwobay/ppapi,rise-worlds/ppapi,xinghaizhou/ppapi,YachaoLiu/ppapi,thdtjsdn/ppapi,lag945/ppapi,dingdayong/ppapi,nanox/ppapi,huochetou999/ppapi,whitewolfm/ppapi,siweilvxing/ppapi,chenfeng8742/ppapi,tiaolong/ppapi,rise-worlds/ppapi,rise-worlds/ppapi,CharlesHuimin/ppapi,huqingyu/ppapi,phisixersai/ppapi,HAfsari/ppapi,stefanie924/ppapi,whitewolfm/ppapi,xuesongzhu/ppapi