[webrtc-stats] Clarify if stat object's members can change after having been returned

stefhak has just created a new issue for 
https://github.com/w3c/webrtc-stats:

== Clarify if stat object's members can change after having been 
returned ==
>From web perf group review [1]:

"Some pieces of the text hint that a Stat object’s members can be 
changed after it is returned. But an example shows 2 objects being 
compared to see how a baseline compares to a later “report”. Can stat 
object’s values be changed after they are returned?

http://www.w3.org/TR/2016/WD-webrtc-stats-20161214/#lifetime-of-stats-objects
 hints that an object that has been returned to JavaScript may change 
between accesses, but I could be misreading it."


[1] 
https://lists.w3.org/Archives/Public/public-web-perf/2016Dec/0014.html

Please view or discuss this issue at 
https://github.com/w3c/webrtc-stats/issues/121 using your GitHub 
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