Add null check for MediaDevicesManager in MDDH destructor.

content/browser/renderer_host/media/media_stream_manager.cc

Index: content/browser/renderer_host/media/media_stream_manager.cc
diff --git a/content/browser/renderer_host/media/media_stream_manager.cc b/content/browser/renderer_host/media/media_stream_manager.cc
index 0da58a4dc1a807af796a83d476c08bf21425803a..887e9e9a0e5fc5c51414b1a5b47656aaa3ace459 100644
--- a/content/browser/renderer_host/media/media_stream_manager.cc
+++ b/content/browser/renderer_host/media/media_stream_manager.cc
@@ -457,7 +457,6 @@ AudioInputDeviceManager* MediaStreamManager::audio_input_device_manager() {
 
 MediaDevicesManager* MediaStreamManager::media_devices_manager() {
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
-  DCHECK(media_devices_manager_.get());

[tommi (sloooow) - chröme, 2017/01/03 15:58:27]

can you add a comment here instead that explains that nullptr may be returned
during shutdown? 

[Guido Urdaneta, 2017/01/03 16:02:49]

Done.

   return media_devices_manager_.get();
 }