WeakPtr destruction order cleanup: media edition.

media/cast/video_sender/external_video_encoder.h

Index: media/cast/video_sender/external_video_encoder.h
diff --git a/media/cast/video_sender/external_video_encoder.h b/media/cast/video_sender/external_video_encoder.h
index 446cac5a4d4e666d1576ce91a799b47d69fe89cc..6359f948643f08a16e6f7025ba05a6644e6b1f2a 100644
--- a/media/cast/video_sender/external_video_encoder.h
+++ b/media/cast/video_sender/external_video_encoder.h
@@ -70,7 +70,8 @@ class ExternalVideoEncoder : public VideoEncoder {
   scoped_refptr<base::SingleThreadTaskRunner> encoder_task_runner_;
 
   // Weak pointer factory for posting back LocalVideoEncodeAcceleratorClient
-  // notifications to ExternalVideoEncoder.
+  // notifications to ExternalVideoEncoder.  NOTE: This must always be last so
+  // it's invalidated before other member variables might be accessed.
   base::WeakPtrFactory<ExternalVideoEncoder> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ExternalVideoEncoder);