Add field VideoEncoderConfig::codec_type.

First step of the transition needed to reland cl
https://webrtc-review.googlesource.com/62062, and move payload_name
and payload_type out of VideoSendStream::Config::EncoderSettings.

If the new field is set to something different than kVideoCodecUnkown,
payload_name from EncoderSettings is ignored.

Bug: webrtc:8830
Change-Id: I515a91f8291cda79017332102cc6a10736d8a648
Reviewed-on: https://webrtc-review.googlesource.com/64001
Reviewed-by: Rasmus Brandt <brandtr@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22555}

modules/video_coding/include/video_codec_initializer.h

@@ -49,8 +49,8 @@ class VideoCodecInitializer {
   static VideoCodec VideoEncoderConfigToVideoCodec(
       const VideoEncoderConfig& config,
       const std::vector<VideoStream>& streams,
-      const std::string& payload_name,
-      int payload_type,
+      // TODO(nisse): Delete when we can rely on config.codec_type.
+      VideoCodecType codec_type,
       bool nack_enabled);
 };