AudioCodingModule: Add methods for injecting external encoder stacks

webrtc/modules/audio_coding/acm2/audio_coding_module_impl.h

Index: webrtc/modules/audio_coding/acm2/audio_coding_module_impl.h
diff --git a/webrtc/modules/audio_coding/acm2/audio_coding_module_impl.h b/webrtc/modules/audio_coding/acm2/audio_coding_module_impl.h
index 102396f70b372375ab7227783eef0f6df4622619..030591b484e7f3ae621095438051ade39964f666 100644
--- a/webrtc/modules/audio_coding/acm2/audio_coding_module_impl.h
+++ b/webrtc/modules/audio_coding/acm2/audio_coding_module_impl.h
@@ -47,6 +47,8 @@ class AudioCodingModuleImpl final : public AudioCodingModule {
   void RegisterExternalSendCodec(
       AudioEncoder* external_speech_encoder) override;
 
+  void VisitEncoder(const EncoderVisitor& ev) override;
+
   // Get current send codec.
   rtc::Optional<CodecInst> SendCodec() const override;
 
@@ -117,9 +119,9 @@ class AudioCodingModuleImpl final : public AudioCodingModule {
   // Get current playout frequency.
   int PlayoutFrequency() const override;
 
-  // Register possible receive codecs, can be called multiple times,
-  // for codecs, CNG, DTMF, RED.
   int RegisterReceiveCodec(const CodecInst& receive_codec) override;
+  int RegisterReceiveCodec(const CodecInst& receive_codec,
+                           const DecoderFactory& df) override;
 
   int RegisterExternalReceiveCodec(int rtp_payload_type,
                                    AudioDecoder* external_decoder,
@@ -211,6 +213,10 @@ class AudioCodingModuleImpl final : public AudioCodingModule {
     const std::string histogram_name_;
   };
 
+  int RegisterReceiveCodecUnlocked(const CodecInst& codec,
+                                   const DecoderFactory& df)
+      EXCLUSIVE_LOCKS_REQUIRED(acm_crit_sect_);
+
   int Add10MsDataInternal(const AudioFrame& audio_frame, InputData* input_data)
       EXCLUSIVE_LOCKS_REQUIRED(acm_crit_sect_);
   int Encode(const InputData& input_data)