Add support for rtx with h264.

webrtc/media/webrtc/webrtcvideoengine2.cc

Index: webrtc/media/webrtc/webrtcvideoengine2.cc
diff --git a/webrtc/media/webrtc/webrtcvideoengine2.cc b/webrtc/media/webrtc/webrtcvideoengine2.cc
index b968322ee3db9d31998bbf513cd9a209bad86ab3..0c52c7526c3b8adf19b1b6cb7855dd5426cc3402 100644
--- a/webrtc/media/webrtc/webrtcvideoengine2.cc
+++ b/webrtc/media/webrtc/webrtcvideoengine2.cc
@@ -336,19 +336,19 @@ std::vector<VideoCodec> DefaultVideoCodecList() {
   std::vector<VideoCodec> codecs;
   codecs.push_back(MakeVideoCodecWithDefaultFeedbackParams(kDefaultVp8PlType,
                                                            kVp8CodecName));
+  codecs.push_back(
+      VideoCodec::CreateRtxCodec(kDefaultRtxVp8PlType, kDefaultVp8PlType));
   if (CodecIsInternallySupported(kVp9CodecName)) {
     codecs.push_back(MakeVideoCodecWithDefaultFeedbackParams(kDefaultVp9PlType,
                                                              kVp9CodecName));
+    codecs.push_back(
+        VideoCodec::CreateRtxCodec(kDefaultRtxVp9PlType, kDefaultVp9PlType));
   }
   if (CodecIsInternallySupported(kH264CodecName)) {
     codecs.push_back(MakeVideoCodecWithDefaultFeedbackParams(kDefaultH264PlType,
                                                              kH264CodecName));
-  }
-  codecs.push_back(
-      VideoCodec::CreateRtxCodec(kDefaultRtxVp8PlType, kDefaultVp8PlType));
-  if (CodecIsInternallySupported(kVp9CodecName)) {
     codecs.push_back(
-        VideoCodec::CreateRtxCodec(kDefaultRtxVp9PlType, kDefaultVp9PlType));
+        VideoCodec::CreateRtxCodec(kDefaultRtxH264PlType, kDefaultH264PlType));
   }
   codecs.push_back(VideoCodec(kDefaultRedPlType, kRedCodecName));
   codecs.push_back(