fix(HlsParser): Fix HLS live stream playback failure
fix(HlsParser): Fix HLS live stream playback failure

Since createSegments_() is asynchronous, and we are updating all the streams
in parallel, the global playlistStartTime_ value may get changed when we update
other playlists, rather than the current playlist. This caused the references'
start and end times discontinuous in a stream.

Closes #2605

Change-Id: Ib2dd1161f4075486f79b0122b98e558ea7d05aaa

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