WebRTC: Use the MediaStream Recording API for the audio_quality_browsertest.

chrome/test/data/webrtc/audio_extraction.js

+/**
+ * Copyright 2017 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.
+ */
+
+/**
+ * Aggregate target bits per second for encoding of the Audio track.
+ * @private
+ */
+const AUDIO_BITS_PER_SECOND = 3000000;
+
+var CAPTURE_STATUS = 'not-started';

[mcasas, 2017/03/22 17:04:55]

This is a true variable, so
s/CAPTURE_STATUS/captureStatus/

+
+/**
+ * Starts the audio capturing.
+ *
+ * @param {Number} The duration of the capture in seconds.
+ */
+function startAudioCapture(capture_duration_in_seconds, output_file) {
+  console.log('Started capturing for ' + capture_duration_in_seconds + 's to '
+      + output_file);
+  var inputElement = document.getElementById('remote-view');
+
+  // |audioBitsPerSecond| must set to a large number to throw as little
+  // information away as possible.
+  var mediaRecorderOptions = {
+    audioBitsPerSecond: AUDIO_BITS_PER_SECOND,
+    mimeType: 'audio/webm',
+  };
+  var stream = inputElement.srcObject;
+  var mediaRecorder = new MediaRecorder(stream, mediaRecorderOptions);
+
+  var audio_chunks = [];
+
+  mediaRecorder.ondataavailable = function(recording) {
+    audio_chunks.push(recording.data);
+  }
+  mediaRecorder.onstop = function() {
+    var audioBlob = new Blob(audio_chunks, {type: 'audio/webm'});
+
+    var url = window.URL.createObjectURL(audioBlob);
+    var a = document.createElement('a');
+    document.body.appendChild(a);
+
+    a.href = url;
+    a.download = output_file;
+    a.click();
+
+    CAPTURE_STATUS = 'done-capturing';
+  }
+
+  mediaRecorder.start();
+  CAPTURE_STATUS = 'started';
+  setTimeout(function() { mediaRecorder.stop(); },
+             capture_duration_in_seconds * 1000);
+
+  returnToTest('ok-capturing');
+}
+
+function getCaptureStatus() {
+  returnToTest(CAPTURE_STATUS);

[mcasas, 2017/03/22 17:04:55]

getCaptureStatus() uses only compare the returned
value with 'done-capturing', and usually having a
string around makes the test hard to maintain in the 
long run (because the code has hidden data dependencies).
I suggest changing CAPTURE_STATUS (or captureStatus) 
to a boolean usage, renaming it to e.g. doneRecording or 
similar, and  s/getCaptureStatus()/isRecordingFinished()/ .

+}