Removed unnecessary VideoTrack creation code in MediaStreamCenter::didCreateMediaStream

MediaStreamCenter::didCreateMediaStream is called from here.
https://code.google.com/p/chromium/codesearch#chromium/src/third_party/WebKit/Source/modules/mediastream/MediaStream.cpp&sq=package:chromium&type=cs&l=146&rcl=1447771613

Before that, the tracks have already been created.

Review URL: https://codereview.chromium.org/1462473002

Cr-Commit-Position: refs/heads/master@{#360554}

content/renderer/media/media_stream_center.cc

@@ -165,16 +165,8 @@ void MediaStreamCenter::didStopLocalMediaStream(
 void MediaStreamCenter::didCreateMediaStream(blink::WebMediaStream& stream) {
   DVLOG(1) << "MediaStreamCenter::didCreateMediaStream";
   blink::WebMediaStream writable_stream(stream);
-  MediaStream* native_stream(
-      new MediaStream(stream));
+  MediaStream* native_stream(new MediaStream(stream));
   writable_stream.setExtraData(native_stream);
-
-  blink::WebVector<blink::WebMediaStreamTrack> video_tracks;
-  stream.videoTracks(video_tracks);
-  for (size_t i = 0; i < video_tracks.size(); ++i) {
-    if (!MediaStreamTrack::GetTrack(video_tracks[i]))
-      CreateNativeMediaStreamTrack(video_tracks[i], rtc_factory_);
-  }
 }
 
 bool MediaStreamCenter::didAddMediaStreamTrack(