Implement a source for remote video tracks.

content/renderer/media/media_stream_video_source.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/renderer/media/media_stream_video_source.h"
 
 #include <algorithm>
 #include <limits>
 #include <string>
 
@@ skipping 290 matching lines @@
       return true;
   }
   return false;
 }
 
 MediaStreamVideoSource::MediaStreamVideoSource(
     MediaStreamDependencyFactory* factory)
     : state_(NEW),
       factory_(factory),
       capture_adapter_(NULL) {
-  DCHECK(factory_);
 }
 
 MediaStreamVideoSource::~MediaStreamVideoSource() {
 }
 
 void MediaStreamVideoSource::AddTrack(
     MediaStreamVideoTrack* track,
     const blink::WebMediaConstraints& constraints,
     const ConstraintsCallback& callback) {
   DCHECK(CalledOnValidThread());
@@ skipping 208 matching lines @@
 MediaStreamVideoSource::RequestedConstraints::RequestedConstraints(
     const blink::WebMediaConstraints& constraints,
     const ConstraintsCallback& callback)
     : constraints(constraints), callback(callback) {
 }
 
 MediaStreamVideoSource::RequestedConstraints::~RequestedConstraints() {
 }
 
 }  // namespace content