We use an increasing player Id as the token between MediaReousrce and MediaDemuxer to
identify which GeckoHlsPlayer should be used.
In this case, playback of 2 HLS content at the same page to make sure the underlying components won't be selected mistakenly
MozReview-Commit-ID: HzrczjsYEoz
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extra : rebase_source : e749788cb6aabd2bdc1ab005829d9377e9acc653
