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 9a48e74d3e5f8f23375228951846f545b0fd7443..91475c9e82f380a87f4ca0415a013995aa98139a 100644
--- a/webrtc/modules/video_coding/codecs/vp9/vp9_impl.h
+++ b/webrtc/modules/video_coding/codecs/vp9/vp9_impl.h
@@ -47,6 +47,8 @@ class VP9EncoderImpl : public VP9Encoder {
 
   void OnDroppedFrame() override {}
 
+  const char* ImplementationName() const override;
+
   struct LayerFrameRefSettings {
     int8_t upd_buf = -1;   // -1 - no update,    0..7 - update buffer 0..7
     int8_t ref_buf1 = -1;  // -1 - no reference, 0..7 - reference buffer 0..7
@@ -148,6 +150,8 @@ class VP9DecoderImpl : public VP9Decoder {
 
   int Reset() override;
 
+  const char* ImplementationName() const override;
+
  private:
   int ReturnFrame(const vpx_image_t* img, uint32_t timeStamp);