Fix: RefCountInterface: Make AddRef() and Release() const

talk/app/webrtc/dtmfsender_unittest.cc

Index: talk/app/webrtc/dtmfsender_unittest.cc
diff --git a/talk/app/webrtc/dtmfsender_unittest.cc b/talk/app/webrtc/dtmfsender_unittest.cc
index ba2e163f1338a35ef739c4a0a7c668ffbe2ac561..f686aa2ccc676c7ef429aa7cc2bac5e9d9aa3a1d 100644
--- a/talk/app/webrtc/dtmfsender_unittest.cc
+++ b/talk/app/webrtc/dtmfsender_unittest.cc
@@ -34,7 +34,6 @@
 #include "talk/app/webrtc/audiotrack.h"
 #include "webrtc/base/gunit.h"
 #include "webrtc/base/logging.h"
-#include "webrtc/base/refcount.h"
 #include "webrtc/base/timeutils.h"
 
 using webrtc::AudioTrackInterface;
@@ -46,7 +45,7 @@ using webrtc::DtmfSenderObserverInterface;
 static const char kTestAudioLabel[] = "test_audio_track";
 static const int kMaxWaitMs = 3000;
 
-class FakeDtmfObserver : public DtmfSenderObserverInterface, RefCountInterface {
+class FakeDtmfObserver : public DtmfSenderObserverInterface {
  public:
   FakeDtmfObserver() : completed_(false) {}