Rewrite WebRtcSession media tests as PeerConnection tests

Bug: webrtc:8222
Change-Id: I782a3227e30de70eb8f6c26a48723cb3510a84ad
Reviewed-on: https://webrtc-review.googlesource.com/6640
Commit-Queue: Steve Anton <steveanton@webrtc.org>
Reviewed-by: Taylor Brandstetter <deadbeef@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20364}

pc/peerconnection_ice_unittest.cc

@@ -120,7 +120,8 @@ class PeerConnectionIceUnitTest : public ::testing::Test {
     if (!wrapper) {
       return nullptr;
     }
-    wrapper->AddAudioVideoStream("s", "a", "v");
+    wrapper->AddAudioTrack("a");
+    wrapper->AddVideoTrack("v");
     return wrapper;
   }