Fix duplicate test names in WebAudio tests

third_party/WebKit/LayoutTests/webaudio/resources/merger-testing.js

 // This file is for the audiochannelmerger-* layout tests.
 // Requires |audio-testing.js| to work properly.
 
 function testMergerInput(config, done) {
   var context = new OfflineAudioContext(config.numberOfChannels, 128, 44100);
   var merger = context.createChannelMerger(config.numberOfChannels);
   var source = context.createBufferSource();
   source.buffer = createConstantBuffer(context, 128, config.testBufferContent);
 
   // Connect the output of source into the specified input of merger.
   if (config.mergerInputIndex)
     source.connect(merger, 0, config.mergerInputIndex);
   else
     source.connect(merger);
   merger.connect(context.destination);
   source.start();
 
   context.startRendering().then(function (buffer) {
+    let prefix = config.testBufferContent.length + '-channel source: ';
     for (var i = 0; i < config.numberOfChannels; i++)
-      Should('Channel #' + i, buffer.getChannelData(i))
+      Should(prefix + 'Channel #' + i, buffer.getChannelData(i))
         .beConstantValueOf(config.expected[i]);
     done();
   });
 }