Log decoder implementation name

Bug: none
Change-Id: I2c6b6a2a62bbcd058b8ed336e6e0f36b8b0d0844
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/175220
Reviewed-by: Erik Språng <sprang@webrtc.org>
Commit-Queue: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31321}

modules/video_coding/generic_decoder.h

@@ -12,6 +12,7 @@
 #define MODULES_VIDEO_CODING_GENERIC_DECODER_H_
 
 #include <memory>
+#include <string>
 
 #include "api/units/time_delta.h"
 #include "modules/video_coding/encoded_frame.h"
@@ -112,6 +113,7 @@ class VCMGenericDecoder {
   VideoCodecType _codecType;
   const bool _isExternal;
   VideoContentType _last_keyframe_content_type;
+  std::string implementation_name_;
 };
 
 }  // namespace webrtc