Check that the source is valid before accessing it in MSVT::GetSettings.

content/renderer/media/media_stream_video_track.cc

Index: content/renderer/media/media_stream_video_track.cc
diff --git a/content/renderer/media/media_stream_video_track.cc b/content/renderer/media/media_stream_video_track.cc
index 143b0c72fd41a2dcd8ca8b98200cc857e2a3cbd8..d5d966d96c02e3e9a3d2eeb586a84e3730a2a307 100644
--- a/content/renderer/media/media_stream_video_track.cc
+++ b/content/renderer/media/media_stream_video_track.cc
@@ -390,16 +390,21 @@ void MediaStreamVideoTrack::Stop() {
 
 void MediaStreamVideoTrack::GetSettings(
     blink::WebMediaStreamTrack::Settings& settings) {
+  DCHECK(main_render_thread_checker_.CalledOnValidThread());
+  if (width_ && height_) {
+    settings.width = width_;
+    settings.height = height_;
+  }

[mcasas, 2017/04/11 17:37:00]

nit: maybe nonsense, but what about

if (width_)
  settings.width = width_;
if (height_)
  settings.height = height_;

[Guido Urdaneta, 2017/04/11 18:40:42]

I think the original intent is to return values only if both are set.
Land as is, since the main purpose of this CL is to fix the bug.

+
+  if (!source_)
+    return;
+
   base::Optional<media::VideoCaptureFormat> format =
       source_->GetCurrentFormat();
   if (format) {
     settings.frame_rate = format->frame_rate;
     settings.video_kind = GetVideoKindForFormat(*format);
   }
-  if (width_ && height_) {
-    settings.width = width_;
-    settings.height = height_;
-  }
   switch (source_->device_info().device.video_facing) {
     case media::MEDIA_VIDEO_FACING_NONE:
       settings.facing_mode = blink::WebMediaStreamTrack::FacingMode::kNone;