Allow a received audio codec's payload type to change.

webrtc/api/audio_codecs/audio_format.h

Index: webrtc/api/audio_codecs/audio_format.h
diff --git a/webrtc/api/audio_codecs/audio_format.h b/webrtc/api/audio_codecs/audio_format.h
index 8814a3dcdcc0c700424f7990c1c6d8b0261c08ae..d8e33426b67c5551852c5c429ae45c676cda2f10 100644
--- a/webrtc/api/audio_codecs/audio_format.h
+++ b/webrtc/api/audio_codecs/audio_format.h
@@ -41,6 +41,11 @@ struct SdpAudioFormat {
                  const Parameters& param);
   ~SdpAudioFormat();
 
+  // Returns true if this format is compatible with |o|. In SDP terminology:
+  // would it represent the same codec between an offer and an answer? As
+  // opposed to operator==, this method disregards codec parameters.
+  bool Matches(const SdpAudioFormat& o) const;
+
   SdpAudioFormat& operator=(const SdpAudioFormat&);
   SdpAudioFormat& operator=(SdpAudioFormat&&);