Expose codec implementation names in stats.

webrtc/video/video_decoder.cc

Index: webrtc/video/video_decoder.cc
diff --git a/webrtc/video/video_decoder.cc b/webrtc/video/video_decoder.cc
index fa1f2ee878045ca9df14f70b3e73be4134d023fd..9ce9088cf84fd4ef43b3371ba6120921cc49e494 100644
--- a/webrtc/video/video_decoder.cc
+++ b/webrtc/video/video_decoder.cc
@@ -76,6 +76,9 @@ bool VideoDecoderSoftwareFallbackWrapper::InitFallbackDecoder() {
   }
   if (callback_ != nullptr)
     fallback_decoder_->RegisterDecodeCompleteCallback(callback_);
+  fallback_implementation_name_ =
+      std::string(fallback_decoder_->ImplementationName()) +
+      " (fallback from: " + decoder_->ImplementationName() + ")";
   return true;
 }
 
@@ -131,4 +134,10 @@ int32_t VideoDecoderSoftwareFallbackWrapper::Reset() {
   return decoder_->Reset();
 }
 
+const char* VideoDecoderSoftwareFallbackWrapper::ImplementationName() const {
+  if (fallback_decoder_)
+    return fallback_implementation_name_.c_str();
+  return decoder_->ImplementationName();
+}
+
 }  // namespace webrtc