This makes the receiver know about its associated set of streams, the equivalent of the [[AssociatedRemoteMediaStreams]] slot in the spec, https://w3c.github.io/webrtc-pc/#dfn-x%5B%5Bassociatedremotemediastreams%5D%5D This does not change layers below peerconnection.cc. The streams are set upon the receiver's construction and is not modified for the duration of its lifetime. When we support modifying the associated set of streams of a receiver the receiver needs to know about it. The receiver's streams() should be used in all places where a receiver's streams need to be known. Bug: webrtc:8473 Change-Id: I31202973aed98e61fa9b6a78b52e815227b6c17d Reviewed-on: https://webrtc-review.googlesource.com/22922 Reviewed-by: Peter Thatcher <pthatcher@webrtc.org> Reviewed-by: Magnus Jedvert <magjed@webrtc.org> Reviewed-by: Steve Anton <steveanton@webrtc.org> Commit-Queue: Henrik Boström <hbos@webrtc.org> Cr-Commit-Position: refs/heads/master@{#20825}