Add AV1 to WebRTC.Video.Encoder.CodecType histogram.

Bug: chromium:1330308
Change-Id: Ifc43f98633cd4f6aa033e6b443680a98f93ab62b
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/264445
Reviewed-by: Philip Eliasson <philipel@webrtc.org>
Reviewed-by: Åsa Persson <asapersson@webrtc.org>
Commit-Queue: Philip Eliasson <philipel@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#37044}

video/send_statistics_proxy.cc

@@ -46,6 +46,7 @@ enum HistogramCodecType {
   kVideoVp8 = 1,
   kVideoVp9 = 2,
   kVideoH264 = 3,
+  kVideoAv1 = 4,
   kVideoMax = 64,
 };
 
@@ -73,6 +74,8 @@ HistogramCodecType PayloadNameToHistogramCodecType(
       return kVideoVp9;
     case kVideoCodecH264:
       return kVideoH264;
+    case kVideoCodecAV1:
+      return kVideoAv1;
     default:
       return kVideoUnknown;
   }