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

content/renderer/media/media_stream_video_track.cc

 // Copyright 2013 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_track.h"
 
 #include <utility>
 
 #include "base/bind.h"
 #include "base/location.h"
@@ skipping 372 matching lines @@
   DCHECK(main_render_thread_checker_.CalledOnValidThread());
   if (source_) {
     source_->RemoveTrack(this);
     source_ = NULL;
   }
   OnReadyStateChanged(blink::WebMediaStreamSource::kReadyStateEnded);
 }
 
 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;
       break;
     case media::MEDIA_VIDEO_FACING_USER:
       settings.facing_mode = blink::WebMediaStreamTrack::FacingMode::kUser;
       break;
     case media::MEDIA_VIDEO_FACING_ENVIRONMENT:
       settings.facing_mode =
           blink::WebMediaStreamTrack::FacingMode::kEnvironment;
@@ skipping 13 matching lines @@
 }
 
 void MediaStreamVideoTrack::OnReadyStateChanged(
     blink::WebMediaStreamSource::ReadyState state) {
   DCHECK(main_render_thread_checker_.CalledOnValidThread());
   for (auto* sink : sinks_)
     sink->OnReadyStateChanged(state);
 }
 
 }  // namespace content