Expose codec implementation names in stats.

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

Index: webrtc/modules/video_coding/codecs/vp9/vp9_impl.cc
diff --git a/webrtc/modules/video_coding/codecs/vp9/vp9_impl.cc b/webrtc/modules/video_coding/codecs/vp9/vp9_impl.cc
index eba8dfb6b19e1d2d3b67072350d717e0ea4b4884..033a3be3974d0cfe11329f27da1c8d24e0151b11 100644
--- a/webrtc/modules/video_coding/codecs/vp9/vp9_impl.cc
+++ b/webrtc/modules/video_coding/codecs/vp9/vp9_impl.cc
@@ -811,6 +811,10 @@ int VP9EncoderImpl::RegisterEncodeCompleteCallback(
   return WEBRTC_VIDEO_CODEC_OK;
 }
 
+const char* VP9EncoderImpl::ImplementationName() const {
+  return "libvpx";
+}
+
 VP9Decoder* VP9Decoder::Create() {
   return new VP9DecoderImpl();
 }
@@ -984,4 +988,9 @@ int VP9DecoderImpl::Release() {
   inited_ = false;
   return WEBRTC_VIDEO_CODEC_OK;
 }
+
+const char* VP9DecoderImpl::ImplementationName() const {
+  return "libvpx";
+}
+
 }  // namespace webrtc