[webrtc-stats] Pull Request: Adding minor clarification regarding stats object lifetime.

taylor-b has just submitted a new pull request for 
https://github.com/w3c/webrtc-stats:

== Adding minor clarification regarding stats object lifetime. ==
A stats object is created at the same time as the underlying object; 
NOT
when getStats is called. That means that if an underlying object is
created and destroyed in-between an application calling getStats, it
should still appear in the stats.

See https://github.com/w3c/webrtc-stats/pull/114