Wrote a test which exercises audio-only WebRTC calls.

content/test/data/media/webrtc_test_audio.js

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Audio test utilities.
 
 // GetStats reports audio output energy in the [0, 32768] range.
 var MAX_AUDIO_OUTPUT_ENERGY = 32768;
 
 // Gathers |numSamples| samples at |frequency| number of times per second and
 // calls back |callback| with an array with numbers in the [0, 32768] range.
 function gatherAudioLevelSamples(peerConnection, numSamples, frequency,
                                  callback) {
-  console.log('Gathering ' + numSamples + ' audio samples...');
+  console.log('Gathering ' + numSamples + ' audio samples (waiting for call ' +
+              'to get up if necessary)...');
   var audioLevelSamples = []
   var gatherSamples = setInterval(function() {
     peerConnection.getStats(function(response) {
-      audioLevelSamples.push(getAudioLevelFromStats_(response));
+      audioOutputLevels = getAudioLevelFromStats_(response);
+      if (audioOutputLevels.length == 0)
+        return;  // The call probably isn't up yet.

[no longer working on chromium, 2014/06/05 09:12:32]

nit, make it look more chromium:
if (audioOutputLevels.length) {
  // The call probably isn't up yet.
  return;
}

[phoglund_chromium, 2014/06/09 06:55:36]

Done.

+
+      // If more than one audio level is reported we get confused.
+      assertEquals(1, audioOutputLevels.length);
+      audioLevelSamples.push(audioOutputLevels[0]);
+
       if (audioLevelSamples.length == numSamples) {
         console.log('Gathered all samples.');
         clearInterval(gatherSamples);
         callback(audioLevelSamples);
       }
     });
   }, 1000 / frequency);
 }
 
 // Tries to identify the beep-every-half-second signal generated by the fake
@@ skipping 47 matching lines @@
  */
 function getAudioLevelFromStats_(response) {
   var reports = response.result();
   var audioOutputLevels = [];
   for (var i = 0; i < reports.length; ++i) {
     var report = reports[i];
     if (report.names().indexOf('audioOutputLevel') != -1) {
       audioOutputLevels.push(report.stat('audioOutputLevel'));
     }
   }
-  // Should only be one audio level reported, otherwise we get confused.
-  assertEquals(1, audioOutputLevels.length);
-
-  return audioOutputLevels[0];
+  return audioOutputLevels;
 }