Expose codec implementation names in stats.

webrtc/modules/video_coding/codecs/vp9/vp9_impl.h

Index: webrtc/modules/video_coding/codecs/vp9/vp9_impl.h
diff --git a/webrtc/modules/video_coding/codecs/vp9/vp9_impl.h b/webrtc/modules/video_coding/codecs/vp9/vp9_impl.h
index c164a63980f2dedf54149e4f6e30477682f947e8..171bc56bb21d34fd1008546bb8f21ebd6be18b60 100644
--- a/webrtc/modules/video_coding/codecs/vp9/vp9_impl.h
+++ b/webrtc/modules/video_coding/codecs/vp9/vp9_impl.h
@@ -45,6 +45,8 @@ class VP9EncoderImpl : public VP9Encoder {
 
   void OnDroppedFrame() override {}
 
+  const char* ImplementationName() const override;
+
  private:
   // Determine number of encoder threads to use.
   int NumberOfThreads(int width, int height, int number_of_cores);
@@ -114,6 +116,8 @@ class VP9DecoderImpl : public VP9Decoder {
 
   int Reset() override;
 
+  const char* ImplementationName() const override;
+
  private:
   int ReturnFrame(const vpx_image_t* img, uint32_t timeStamp);