This will make it much less likely for application developers to not
realize the object is reference counted.
It also fixes a bug in the Java PeerConnection binding, by allowing a
reference to be transferred in the OnRemoveStream call via std::move.
BUG=webrtc:5128
R=pthatcher@webrtc.org, tkchin@webrtc.org
Review URL: https://codereview.webrtc.org/1972793003 .
Cr-Commit-Position: refs/heads/master@{#12976}