Introduce struct MediaConfig, with construction-time settings.

talk/app/webrtc/statscollector_unittest.cc

Index: talk/app/webrtc/statscollector_unittest.cc
diff --git a/talk/app/webrtc/statscollector_unittest.cc b/talk/app/webrtc/statscollector_unittest.cc
index 1b16b0c4fa7914fa58b8fea5805ed02fc8a932bc..06af23752e9d8323fea15e3edd7fcc083f130812 100644
--- a/talk/app/webrtc/statscollector_unittest.cc
+++ b/talk/app/webrtc/statscollector_unittest.cc
@@ -507,6 +507,7 @@ class StatsCollectorTest : public testing::Test {
             new cricket::ChannelManager(media_engine_, rtc::Thread::Current())),
         media_controller_(
             webrtc::MediaControllerInterface::Create(rtc::Thread::Current(),
+                                                     webrtc::MediaConfig(),
                                                      channel_manager_.get())),
         session_(media_controller_.get()) {
     // By default, we ignore session GetStats calls.