WebRtcVideoEngine: Enable encoded frame sink.

This change ultimately enables wiring up VideoRtpReceiver::OnGenerateKeyFrame
and OnEncodedSinkEnabled into internal::VideoReceiveStream so that encoded
frames can flow to sinks installed in VideoTrackSourceInterface.

Bug: chromium:1013590
Change-Id: I136132c210e5811547f2522ddc371d0acac90664
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/161093
Commit-Queue: Markus Handell <handellm@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30001}
diff --git a/media/base/fake_media_engine.h b/media/base/fake_media_engine.h
index 99a9b49..aa713d0 100644
--- a/media/base/fake_media_engine.h
+++ b/media/base/fake_media_engine.h
@@ -436,6 +436,13 @@
   absl::optional<int> GetBaseMinimumPlayoutDelayMs(
       uint32_t ssrc) const override;
 
+  void SetRecordableEncodedFrameCallback(
+      uint32_t ssrc,
+      std::function<void(const webrtc::RecordableEncodedFrame&)> callback)
+      override;
+  void ClearRecordableEncodedFrameCallback(uint32_t ssrc) override;
+  void GenerateKeyFrame(uint32_t ssrc) override;
+
  private:
   bool SetRecvCodecs(const std::vector<VideoCodec>& codecs);
   bool SetSendCodecs(const std::vector<VideoCodec>& codecs);