Make VideoFrameType an enum class, and move to separate file and target

Bug: webrtc:5876, webrtc:6883
Change-Id: I1435cfa9e8e54c4ba2978261048ff3fbb993ce0e
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/126225
Commit-Queue: Niels Moller <nisse@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27239}
diff --git a/modules/video_coding/generic_decoder.cc b/modules/video_coding/generic_decoder.cc
index 6ef4c36..dd23066 100644
--- a/modules/video_coding/generic_decoder.cc
+++ b/modules/video_coding/generic_decoder.cc
@@ -220,7 +220,7 @@
   // Set correctly only for key frames. Thus, use latest key frame
   // content type. If the corresponding key frame was lost, decode will fail
   // and content type will be ignored.
-  if (frame.FrameType() == kVideoFrameKey) {
+  if (frame.FrameType() == VideoFrameType::kVideoFrameKey) {
     _frameInfos[_nextFrameInfoIdx].content_type = frame.contentType();
     _last_keyframe_content_type = frame.contentType();
   } else {