Add note that SDP munging is a deprecated unsupported feature (#1710)

and show the error.

Author: fippo

src/content/peerconnection/munge-sdp/index.html

@@ -57,6 +57,10 @@ <h1><a href="//webrtc.github.io/samples/" title="WebRTC samples homepage">WebRTC
         <button id="setAnswer" disabled>Set answer</button>
         <button id="hangup" disabled>Hang up</button>
     </div>
+    <p><b>Note:</b> SDP "munging", i.e. modifying the SDP between <i>createOffer</i>/<i>createAnswer</i> and <i>setLocalDescription</i>
+      is a nonstandard feature which may not work as expected. While some browsers support some modifications,
+      <a href="https://w3c.github.io/webrtc-pc/#dom-peerconnection-setlocaldescription">the W3C standard</a> forbids it.</p>
+    <p id="munge-error"></p>
 
     <div id="preview">
         <div id="local">

src/content/peerconnection/munge-sdp/js/main.js

@@ -138,17 +138,16 @@ function createPeerConnection() {
   if (audioTracks.length > 0) {
     console.log(`Using audio device: ${audioTracks[0].label}`);
   }
-  const servers = null;
 
-  localPeerConnection = new RTCPeerConnection(servers);
+  localPeerConnection = new RTCPeerConnection();
   console.log('Created local peer connection object localPeerConnection');
   localPeerConnection.onicecandidate = e => onIceCandidate(localPeerConnection, e);
   sendChannel = localPeerConnection.createDataChannel('sendDataChannel', dataChannelOptions);
   sendChannel.onopen = onSendChannelStateChange;
   sendChannel.onclose = onSendChannelStateChange;
   sendChannel.onerror = onSendChannelStateChange;
 
-  remotePeerConnection = new RTCPeerConnection(servers);
+  remotePeerConnection = new RTCPeerConnection();
   console.log('Created remote peer connection object remotePeerConnection');
   remotePeerConnection.onicecandidate = e => onIceCandidate(remotePeerConnection, e);
   remotePeerConnection.ontrack = gotRemoteStream;
@@ -165,6 +164,7 @@ function onSetSessionDescriptionSuccess() {
 
 function onSetSessionDescriptionError(error) {
   console.log(`Failed to set session description: ${error.toString()}`);
+  document.getElementById('munge-error').innerText = error.toString();
 }
 
 async function createOffer() {