Only evict per content type.
Only evict per content type.

If a user agent seeks backwards while one media state is idle and
another is updating, the former media state may insert a segment
at the seek target while the latter removes it during eviction.

This race condition is resolved by simply evicting per content type.

Change-Id: I63d315cb8d809de7693e1490b8234053d7dde5cf

indiereign/shaka-player,tvoli/shaka-player,tvoli/shaka-player,indiereign/shaka-player,shaka-project/shaka-player,vimond/shaka-player,TobbeEdgeware/shaka-player,Ross-cz/shaka-player,tvoli/shaka-player,brightcove/shaka-player,brightcove/shaka-player,shaka-project/shaka-player,indiereign/shaka-player,ustudio/shaka-player,ustudio/shaka-player,baconz/shaka-player,ustudio/shaka-player,tvoli/shaka-player,baconz/shaka-player,russitto/shaka-player,Ross-cz/shaka-player,TheModMaker/shaka-player,russitto/shaka-player,TheModMaker/shaka-player,Ross-cz/shaka-player,TheModMaker/shaka-player,TobbeEdgeware/shaka-player,TheModMaker/shaka-player,TobbeEdgeware/shaka-player,vimond/shaka-player,shaka-project/shaka-player,brightcove/shaka-player,russitto/shaka-player,shaka-project/shaka-player,baconz/shaka-player,vimond/shaka-player,ustudio/shaka-player