Update MediaSource polyfills for Safari 10
Update MediaSource polyfills for Safari 10

Safari 10 has some new MediaSource implementation bugs that need to
be worked around.  This updates and refactors the polyfills for Safari
10.

Bugs filed:
  https://goo.gl/qCeTZr
  https://goo.gl/rC3CLj

Closes #615

Change-Id: Id694798cd083878f337c0ba6e017fcdaac3c69be

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