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

The landed CL contained some unwanted changes.

TBR=tommi

Review URL: https://codereview.webrtc.org/1401743002 .

Cr-Commit-Position: refs/heads/master@{#10255}
diff --git a/talk/app/webrtc/dtmfsender_unittest.cc b/talk/app/webrtc/dtmfsender_unittest.cc
index ba2e163..f686aa2 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 @@
 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) {}
 
diff --git a/webrtc/base/refcount.h b/webrtc/base/refcount.h
index dbad2eb..55ce23a 100644
--- a/webrtc/base/refcount.h
+++ b/webrtc/base/refcount.h
@@ -95,11 +95,11 @@
   : T(p1, p2, p3, p4, p5, p6, p7, p8, p9, p10, p11), ref_count_(0) {
   }
 
-  int AddRef() const override {
+  virtual int AddRef() const {
     return AtomicOps::Increment(&ref_count_);
   }
 
-  int Release() const override {
+  virtual int Release() const {
     int count = AtomicOps::Decrement(&ref_count_);
     if (!count) {
       delete this;