MediaRecorder: add and wire read {video,audio}BitsPerSecond props

third_party/WebKit/LayoutTests/fast/mediarecorder/MediaRecorder-creation.html

 <!DOCTYPE html>
 <script src=../../resources/testharness.js></script>
 <script src=../../resources/testharnessreport.js></script>
 <script>
 // This test verifies that MediaRecorder can be created with different Media
 // Stream Track combinations: 1 Video Track only, 1 Audio Track only and finally
 // a Media Stream with both a Video and an Audio Track. Note that recording is
 // _not_ started in this test, see MediaRecorder-basic-video.html for it.
 
 function makeAsyncTest(constraints, verifyStream, message) {
     return async_test(function(test) {
 
         var gotStream = test.step_func(function(stream) {
             verifyStream(stream);
 
             try {
                 recorder = new MediaRecorder(stream);
             } catch (e) {
                 assert_unreached('Exception while creating MediaRecorder: ' + e);
             }
             assert_equals(recorder.state, "inactive");
+            assert_equals(recorder.videoBitsPerSecond, 0);

[philipj_slow, 2016/02/03 03:31:05]

That seems weird, why shouldn't this return the default bitrate being targeted,
just like mimeType should return the default MIME type chosen?

[mcasas, 2016/02/03 23:50:27]

Because the bitrate, when left by JS as undefined,
means is left to the encoder. In this case, it basically
means 0 to signify that the encoders were left to 
decide it (and update it as they see fit). Sense?

[philipj_slow, 2016/02/04 03:03:10]

Well, the encoder isn't really targeting a zero bitrate, why not set it to the
actually targeted bitrate? The reasoning being that creating a new
MediaRecorder({ audioBitsPerSecond: other.audioBitsPerSecond,
videoBitsPerSecond: other.videoBitsPerSecond }) should result exactly the same
bitrate config as other, and it's reasonable to leave zero to mean "minimum
bitrate possible."

+            assert_equals(recorder.audioBitsPerSecond, 0);
             test.done();
         });
 
         var onError = test.step_func(function() {
             assert_unreached('Error creating MediaRecorder.');
         });
 
         try {
             navigator.webkitGetUserMedia(constraints, gotStream, onError);
         } catch(e) {
@@ skipping 18 matching lines @@
     assert_equals(stream.getVideoTracks()[0].readyState, 'live');
     assert_equals(stream.getAudioTracks()[0].readyState, 'live');
 }
 
 // Note: webkitGetUserMedia() must be called with at least video or audio true.
 makeAsyncTest({video:true}, verifyVideoOnlyStream, 'Video only MediaRecorder');
 makeAsyncTest({audio:true}, verifyAudioOnlyStream, 'Audio only MediaRecorder');
 makeAsyncTest({audio:true, video:true}, verifyAudioVideoStream, 'Video and Audio MediaRecorder');
 
 </script>