Allow default video receive channel to receive on any unsignalled SSRC,

webrtc/media/engine/webrtcvideoengine2.cc

Index: webrtc/media/engine/webrtcvideoengine2.cc
diff --git a/webrtc/media/engine/webrtcvideoengine2.cc b/webrtc/media/engine/webrtcvideoengine2.cc
index df796daedd01418962e12268b54ee386c5051016..fc8760b8503f2913202c9b698728dfb921afd4e8 100644
--- a/webrtc/media/engine/webrtcvideoengine2.cc
+++ b/webrtc/media/engine/webrtcvideoengine2.cc
@@ -428,9 +428,8 @@ DefaultUnsignalledSsrcHandler::DefaultUnsignalledSsrcHandler()
 UnsignalledSsrcHandler::Action DefaultUnsignalledSsrcHandler::OnUnsignalledSsrc(
     WebRtcVideoChannel2* channel,
     uint32_t ssrc) {
-  if (default_recv_ssrc_ != 0) {  // Already one default stream.
-    LOG(LS_WARNING) << "Unknown SSRC, but default receive stream already set.";
-    return kDropPacket;
+  if (default_recv_ssrc_ != 0) {  // Already one default stream, so replace it.
+    channel->RemoveRecvStream(default_recv_ssrc_);
   }
 
   StreamParams sp;