Revert of Remove unnecessary interface TelephoneEventHandler

webrtc/modules/rtp_rtcp/source/rtp_receiver_audio.h

Index: webrtc/modules/rtp_rtcp/source/rtp_receiver_audio.h
diff --git a/webrtc/modules/rtp_rtcp/source/rtp_receiver_audio.h b/webrtc/modules/rtp_rtcp/source/rtp_receiver_audio.h
index c1bccc2087f455b46efcba6187c5c6b5dac67efe..d5d89bae2d4c2f233953cef1033324662bf7a45e 100644
--- a/webrtc/modules/rtp_rtcp/source/rtp_receiver_audio.h
+++ b/webrtc/modules/rtp_rtcp/source/rtp_receiver_audio.h
@@ -23,13 +23,23 @@
 namespace webrtc {
 
 // Handles audio RTP packets. This class is thread-safe.
-class RTPReceiverAudio : public RTPReceiverStrategy {
+class RTPReceiverAudio : public RTPReceiverStrategy,
+                         public TelephoneEventHandler {
  public:
   explicit RTPReceiverAudio(RtpData* data_callback);
   virtual ~RTPReceiverAudio() {}
 
+  // The following three methods implement the TelephoneEventHandler interface.
+  // Forward DTMFs to decoder for playout.
+  void SetTelephoneEventForwardToDecoder(bool forward_to_decoder) override;
+
+  // Is forwarding of outband telephone events turned on/off?
+  bool TelephoneEventForwardToDecoder() const override;
+
   // Is TelephoneEvent configured with payload type payload_type
-  bool TelephoneEventPayloadType(const int8_t payload_type) const;
+  bool TelephoneEventPayloadType(const int8_t payload_type) const override;
+
+  TelephoneEventHandler* GetTelephoneEventHandler() override { return this; }
 
   // Returns true if CNG is configured with payload type payload_type. If so,
   // the frequency and cng_payload_type_has_changed are filled in.