This removes use of the MockPeerConnection and replaces it with the
FakePeerConnectionForStats testing class.
Bug: webrtc:8764
Change-Id: I78553c5a4e4d68cb6666a83f443f72f7c25488dc
Reviewed-on: https://webrtc-review.googlesource.com/46940
Commit-Queue: Steve Anton <steveanton@webrtc.org>
Reviewed-by: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Taylor Brandstetter <deadbeef@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#21882}