Mark template class RefCountedObject as final.

pc/rtpsender.h

Index: pc/rtpsender.h
diff --git a/pc/rtpsender.h b/pc/rtpsender.h
index 672637f38540bf2b8ceb2900eb4aa7d05fc5eb57..e40ac6aae6f6c5bbf55f0d2610855bb00adbacef 100644
--- a/pc/rtpsender.h
+++ b/pc/rtpsender.h
@@ -77,7 +77,7 @@ class LocalAudioSinkAdapter : public AudioTrackSinkInterface,
 
 class AudioRtpSender : public DtmfProviderInterface,
                        public ObserverInterface,
-                       public rtc::RefCountedObject<RtpSenderInternal> {
+                       public RtpSenderInternal {
  public:
   // StatsCollector provided so that Add/RemoveLocalAudioTrack can be called
   // at the appropriate times.
@@ -176,8 +176,7 @@ class AudioRtpSender : public DtmfProviderInterface,
   std::unique_ptr<LocalAudioSinkAdapter> sink_adapter_;
 };
 
-class VideoRtpSender : public ObserverInterface,
-                       public rtc::RefCountedObject<RtpSenderInternal> {
+class VideoRtpSender : public ObserverInterface, public RtpSenderInternal {
  public:
   // |channel| can be null if one does not exist yet.
   VideoRtpSender(VideoTrackInterface* track,