Add some more ES6 changes in HlsParser.
Add some more ES6 changes in HlsParser.

Issue #1157

Change-Id: I6869b66665a44408d678a810255096076e93bea5

tvoli/shaka-player,shaka-project/shaka-player,tvoli/shaka-player,tvoli/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player