ObjC: Add implementationName for injectable codecs

webrtc/sdk/objc/Framework/Classes/PeerConnection/RTCVideoCodecH264.mm

Index: webrtc/sdk/objc/Framework/Classes/PeerConnection/RTCVideoCodecH264.mm
diff --git a/webrtc/sdk/objc/Framework/Classes/PeerConnection/RTCVideoCodecH264.mm b/webrtc/sdk/objc/Framework/Classes/PeerConnection/RTCVideoCodecH264.mm
index 7b38ec047cec1dfd2f1ee3080e91b7982117f077..b1fcd1b8a6d516d899f4d31b8141934318001252 100644
--- a/webrtc/sdk/objc/Framework/Classes/PeerConnection/RTCVideoCodecH264.mm
+++ b/webrtc/sdk/objc/Framework/Classes/PeerConnection/RTCVideoCodecH264.mm
@@ -181,6 +181,10 @@ class H264VideoToolboxDecodeCompleteCallback : public webrtc::DecodedImageCallba
                                                                high:kHighH264QpThreshold];
 }
 
+- (NSString *)implementationName {
+  return @"VideoToolbox";
+}
+
 @end
 
 // Decoder.
@@ -247,6 +251,10 @@ class H264VideoToolboxDecodeCompleteCallback : public webrtc::DecodedImageCallba
       image, missingFrames, header.release(), &codecSpecificInfo, renderTimeMs);
 }
 
+- (NSString *)implementationName {
+  return @"VideoToolbox";
+}
+
 @end
 
 // Encoder factory.