WebRTC: Use the MediaStream Recording API for the audio_quality_browsertest.

chrome/test/data/webrtc/audio_extraction.js

+/**
+ * Copyright (c) 2017 The Chromium Authors. All rights reserved.

[mcasas, 2017/03/21 16:54:22]

No (c):

https://chromium.googlesource.com/chromium/src/+/master/styleguide/c++/c++.md...

+ * 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
+ */
+var gAudioBitsPerSecond = 3000000;

[mcasas, 2017/03/21 16:54:22]

gVarName for global variables is atypical in
javascript-in-Chromium. Instead, use 
NAMES_LIKE_THIS for such variables [1]
and make them const (since here we don't
have to think about Internet Explorer).

[1]
https://google.github.io/styleguide/javascriptguide.xml?showone=Constants#Con...

+
+/**
+ * The duration of the audio recording in milliseconds.
+ * @private
+ */
+var gCaptureDuration = 0;

[mcasas, 2017/03/21 16:54:22]

s/gCaptureDuration/captureDurationMs/

but for its usage below, I think we don't need a
file-scope variable and you can just define it in
l.52 as 
const capture_duration_ms = duration * 1000 /* ms per second */;;

+
+/**
+ * The recorded audio encoded in Base64.
+ * @private
+ */
+var gAudioBase64 = '';

[mcasas, 2017/03/21 16:54:22]

s/gAudioBase64/audio_as_base64/

This can be a huge string (slow test, flaky?), and 
anyway you'll be writing it to disk in the .cpp file, 
so perhaps you could consider writing it to disk 
directly (might need some tweaking to the test 
http server).

[ehmaldonado_chromium, 2017/03/21 16:59:55]

Are there any examples of this already?

+
+/**
+ * Chunks of the audio recorded by MediaRecorded as they become available.
+ * @private
+ */
+var gChunks = [];
+
+/**
+ * A string to be returned to the test about the current status of capture.
+ */
+var gCapturingStatus = 'capturing-not-started';
+
+/**
+ * Starts the audio capturing.
+ *
+ * @param {Number} The duration of the capture in seconds.
+ */
+function startAudioCapture(duration) {

[mcasas, 2017/03/21 16:54:22]

s/duration/duration_seconds/ or similar?

+  console.log('started-capture');
+  var inputElement = document.getElementById('remote-view');
+
+  // |audioBitsPerSecond| must set to a large number to throw as little
+  // information away as possible.
+  var mediaRecorderOptions = {
+    audioBitsPerSecond: gAudioBitsPerSecond,
+    mimeType: 'audio/webm',
+  };
+  var stream = getStreamFromElement_(inputElement);
+  gCaptureDuration = 1000 * duration;
+
+  var mediaRecorder = new MediaRecorder(stream, mediaRecorderOptions);
+
+  mediaRecorder.ondataavailable = function(recording) {
+    gChunks.push(recording.data);
+  }
+  mediaRecorder.onstop = function() {
+    console.log(gChunks.length);
+    var audioBlob = new Blob(gChunks, {type: "audio/webm"});
+    gChunks = [];
+    var reader = new FileReader();
+    reader.onloadend = function() {
+      gAudioBase64 = reader.result.substr(reader.result.indexOf(',') + 1);
+      gCapturingStatus = 'done-capturing';
+      debug('done-capturing');
+    }
+    reader.readAsDataURL(audioBlob);
+  }
+
+  mediaRecorder.start();
+  setTimeout(function() { mediaRecorder.stop(); }, gCaptureDuration);
+  gCapturingStatus = 'still-capturing';
+}
+
+/**
+ * Returns the audio recorded by RecordMedia encoded in Base64.
+ */
+function getRecordedAudioAsBase64() {
+  silentReturnToTest(gAudioBase64);
+}
+
+/**
+ * Queries if we're done with the capturing yet.
+ */
+function doneCapturingAudio() {
+  returnToTest(gCapturingStatus);
+}
+
+/**
+ * Returns the stream from the input element to be attached to MediaRecorder.
+ * @private
+ */
+function getStreamFromElement_(element) {
+  if (element.srcObject !== undefined) {
+    return element.srcObject;
+  } else if (element.src !== undefined) {
+    return element.src;
+  } else {
+    failTest('Error extracting stream from element.');
+  }

[mcasas, 2017/03/21 16:54:22]

It's pervasive in Chromium to not have {}
when the bodies are one-liners.  Haven't
found the equivalent in the JS style guide,
but I think it's reasonable, plz consider it.

+}