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..4bdb924727a4267c83964045242898315620cdab 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,

[the sun, 2017/04/26 07:44:10]

super nit: end in ":", not ","

oh well... :)

[Taylor Brandstetter, 2017/04/26 23:04:40]

Done.

+  // 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;

[the sun, 2017/04/26 07:44:09]

More importantly though, can we deprecate operator==()? And are there current
uses of operator==() which should really be Matches()?

[Taylor Brandstetter, 2017/04/26 23:04:40]

It has some existing uses (decoder_database.cc and acm_receiver.cc) that seem
intentional. Checking if a format is exactly equal and whether it "matches" both
seem like reasonable things to do in different situations.

+
   SdpAudioFormat& operator=(const SdpAudioFormat&);
   SdpAudioFormat& operator=(SdpAudioFormat&&);