Parameterize WebRtcSetDescriptionObserverHandlerTest.

Handlers exists in two flavors, WebRtcSetLocalDescriptionObserverHandler
which is used for setLocalDescription(), and
WebRtcSetRemoteDescriptionObserverHandler which is used for
setRemoteDescription(). They have the same functionality but have to be
different classes due to webrtc observer interfaces being different
classes.

Each handler can operate in two modes: surfacing transceiver states
(includes senders and receivers) or only surfacing receiver states.

Prior to this CL, only the "remote" handler and "receiver only" mode
was tested. With this CL, all four combinations
"(local/remote) x (transceivers/receivers)" are tested using
parameterized gtests.

This improves test coverage and unblocks testing that is needed to solve
a bug related to surfacing transceivers (https://crbug.com/897251).

Bug: 865006
Change-Id: Iaf40b498b0fef0978c4179c47118f6cff0bcdf66
Reviewed-on: https://chromium-review.googlesource.com/c/1309747
Commit-Queue: Henrik Boström <hbos@chromium.org>
Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605350}

content/renderer/media/webrtc/mock_peer_connection_impl.cc

@@ -182,6 +182,13 @@ FakeRtpReceiver::streams() const {
   return streams_;
 }
 
+std::vector<std::string> FakeRtpReceiver::stream_ids() const {
+  std::vector<std::string> stream_ids;
+  for (const auto& stream : streams_)
+    stream_ids.push_back(stream->id());
+  return stream_ids;
+}
+
 cricket::MediaType FakeRtpReceiver::media_type() const {
   NOTIMPLEMENTED();
   return cricket::MEDIA_TYPE_AUDIO;

content/renderer/media/webrtc/mock_peer_connection_impl.h

@@ -56,6 +56,7 @@ class FakeRtpReceiver : public webrtc::RtpReceiverInterface {
   rtc::scoped_refptr<webrtc::MediaStreamTrackInterface> track() const override;
   std::vector<rtc::scoped_refptr<webrtc::MediaStreamInterface>> streams()
       const override;
+  std::vector<std::string> stream_ids() const override;
   cricket::MediaType media_type() const override;
   std::string id() const override;
   webrtc::RtpParameters GetParameters() const override;