Expose codec implementation names in stats.

webrtc/video_encoder.h

Index: webrtc/video_encoder.h
diff --git a/webrtc/video_encoder.h b/webrtc/video_encoder.h
index a512c9891791d0d7905e164bf51562ee31dc9e09..59c15751b80fe65b6632f208efd5e5eac56c6ddf 100644
--- a/webrtc/video_encoder.h
+++ b/webrtc/video_encoder.h
@@ -127,6 +127,7 @@ class VideoEncoder {
   virtual void OnDroppedFrame() {}
   virtual int GetTargetFramerate() { return -1; }
   virtual bool SupportsNativeHandle() const { return false; }
+  virtual const char* ImplementationName() const { return "unknown"; }
 };
 
 // Class used to wrap external VideoEncoders to provide a fallback option on
@@ -154,6 +155,7 @@ class VideoEncoderSoftwareFallbackWrapper : public VideoEncoder {
   void OnDroppedFrame() override;
   int GetTargetFramerate() override;
   bool SupportsNativeHandle() const override;
+  const char* ImplementationName() const override;
 
  private:
   const EncoderType encoder_type_;