Added a builtin audio decoder factory to the default PeerConnectionFactory constructor.

webrtc/api/peerconnectionfactory.cc

Index: webrtc/api/peerconnectionfactory.cc
diff --git a/webrtc/api/peerconnectionfactory.cc b/webrtc/api/peerconnectionfactory.cc
index 08fe952abdd2a9605efc7ed8aca9a376c73907ac..745de3f214f748e179710128573e09dbb880fb1a 100644
--- a/webrtc/api/peerconnectionfactory.cc
+++ b/webrtc/api/peerconnectionfactory.cc
@@ -85,7 +85,8 @@ PeerConnectionFactory::PeerConnectionFactory()
       wraps_current_thread_(false),
       network_thread_(rtc::Thread::CreateWithSocketServer().release()),
       worker_thread_(rtc::Thread::Create().release()),
-      signaling_thread_(rtc::Thread::Current()) {
+      signaling_thread_(rtc::Thread::Current()),
+      audio_decoder_factory_(CreateBuiltinAudioDecoderFactory()) {
   if (!signaling_thread_) {
     signaling_thread_ = rtc::ThreadManager::Instance()->WrapCurrentThread();
     wraps_current_thread_ = true;