WebRtcVideoChannel encoder fallback.

In this CL:
 - Added WEBRTC_VIDEO_CODEC_ENCODER_FAILURE return code that can
   be returned by the encoder wrapper in case of a broken encoder.
 - Added EncoderFailureCallback interface that can be called
   to request encoder fallback to be performed. Implemented by
   WebRtcVideoChannel and called from the VideoStreamEncoder.
 - Updated SelectSendVideoCodec to select all compatible codecs instead
   of just one.

Bug: webrtc:10795
Change-Id: I87a83fd02e48c40493c930471c06c3d0941031ab
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/140888
Commit-Queue: Philip Eliasson <philipel@webrtc.org>
Reviewed-by: Magnus Jedvert <magjed@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#28462}

api/video/video_stream_encoder_settings.h

@@ -17,6 +17,12 @@
 
 namespace webrtc {
 
+class EncoderFailureCallback {
+ public:
+  virtual ~EncoderFailureCallback() {}
+  virtual void OnEncoderFailure() = 0;
+};
+
 struct VideoStreamEncoderSettings {
   explicit VideoStreamEncoderSettings(
       const VideoEncoder::Capabilities& capabilities)
@@ -29,6 +35,9 @@ struct VideoStreamEncoderSettings {
   // Ownership stays with WebrtcVideoEngine (delegated from PeerConnection).
   VideoEncoderFactory* encoder_factory = nullptr;
 
+  // Notifies the WebRtcVideoChannel that the currently used encoder is broken.
+  EncoderFailureCallback* encoder_failure_callback = nullptr;
+
   // Ownership stays with WebrtcVideoEngine (delegated from PeerConnection).
   VideoBitrateAllocatorFactory* bitrate_allocator_factory = nullptr;