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 59574aeda911061847be634870b38a179c5f7e82..2b4a4e8cc6236d1f3a3b721b0acefac9570edf2f 100644
--- a/webrtc/modules/video_coding/codecs/vp9/vp9_impl.cc
+++ b/webrtc/modules/video_coding/codecs/vp9/vp9_impl.cc
@@ -608,6 +608,10 @@ int VP9EncoderImpl::RegisterEncodeCompleteCallback(
   return WEBRTC_VIDEO_CODEC_OK;
 }
 
+const char* VP9EncoderImpl::ImplementationName() const {
+  return "libvpx";
+}
+
 VP9Decoder* VP9Decoder::Create() {
   return new VP9DecoderImpl();
 }
@@ -781,4 +785,9 @@ int VP9DecoderImpl::Release() {
   inited_ = false;
   return WEBRTC_VIDEO_CODEC_OK;
 }
+
+const char* VP9DecoderImpl::ImplementationName() const {
+  return "libvpx";
+}
+
 }  // namespace webrtc