Use enum class for VideoCodecMode and VideoCodecComplexity.

Bug: webrtc:7660
Change-Id: I6a8ef01f8abcc25c8efaf0af387408343a7c8ba3
Reviewed-on: https://webrtc-review.googlesource.com/81240
Commit-Queue: Niels Moller <nisse@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23595}
diff --git a/api/video_codecs/video_codec.cc b/api/video_codecs/video_codec.cc
index f429996..c5d9ea9 100644
--- a/api/video_codecs/video_codec.cc
+++ b/api/video_codecs/video_codec.cc
@@ -79,7 +79,7 @@
       numberOfSimulcastStreams(0),
       simulcastStream(),
       spatialLayers(),
-      mode(kRealtimeVideo),
+      mode(VideoCodecMode::kRealtimeVideo),
       expect_encode_from_texture(false),
       timing_frame_thresholds({0, 0}),
       codec_specific_() {}