title: ChannelMergerNode in Web audio API not merging channels
body: <p>I'm trying to use the web audio API to create an audio stream with the left and right channels generated with different oscillators. The output of the left channel is correct, but the right channel is 0. Based on the spec, I can't see what I'm doing wrong.</p>
  
  <p>Tested in Chrome dev.</p>
  
  <p>Code:</p>
  
  <pre><code>var context = new AudioContext();
  var l_osc = context.createOscillator();
  l_osc.type = "sine";
  l_osc.frequency.value = 100;
  var r_osc = context.createOscillator();
  r_osc.type = "sawtooth";
  r_osc.frequency.value = 100;
  // Combine the left and right channels.
  var merger = context.createChannelMerger(2);
  merger.channelCountMode = "explicit";
  merger.channelInterpretation = "discrete";
  l_osc.connect(merger, 0, 0);
  r_osc.connect(merger, 0, 1);
  var dest_stream = context.createMediaStreamDestination();
  merger.connect(dest_stream);
  // Dump the generated waveform to a MediaStream output.
  l_osc.start();
  r_osc.start();
  var track = dest_stream.stream.getAudioTracks()[0];
  var plugin = document.getElementById('plugin');
  plugin.postMessage(track);
  </code></pre>