Make rendering of MediaStreams reflect changes to its set of tracks.

content/shell/test_runner/mock_web_user_media_client.cc

Index: content/shell/test_runner/mock_web_user_media_client.cc
diff --git a/content/shell/test_runner/mock_web_user_media_client.cc b/content/shell/test_runner/mock_web_user_media_client.cc
index e5de05729bd4588462741f6cd27720518055c9b4..77066d3173df81138824c405f5c2941cb3cf17ed 100644
--- a/content/shell/test_runner/mock_web_user_media_client.cc
+++ b/content/shell/test_runner/mock_web_user_media_client.cc
@@ -33,8 +33,6 @@ using blink::WebVector;
 
 namespace test_runner {
 
-class MockExtraData : public WebMediaStream::ExtraData {};
-
 MockWebUserMediaClient::MockWebUserMediaClient(WebTestDelegate* delegate)
     : delegate_(delegate),
       should_enumerate_extra_device_(false),
@@ -57,7 +55,6 @@ void MockWebUserMediaClient::RequestUserMedia(
   WebMediaStream stream;
   stream.Initialize(WebVector<WebMediaStreamTrack>(),
                     WebVector<WebMediaStreamTrack>());
-  stream.SetExtraData(new MockExtraData());
 
   if (request.Audio() &&
       !delegate_->AddMediaStreamAudioSourceAndTrack(&stream)) {