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