Implement NullVideoDecoder to avoid crash on unsupported decoders.

talk/media/webrtc/webrtcvideoengine2.cc

 /*
  * libjingle
  * Copyright 2014 Google Inc.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
  *
  *  1. Redistributions of source code must retain the above copyright notice,
  *     this list of conditions and the following disclaimer.
  *  2. Redistributions in binary form must reproduce the above copyright notice,
@@ skipping 2240 matching lines @@
   if (type == webrtc::kVideoCodecVP9) {
     return AllocatedDecoder(
         webrtc::VideoDecoder::Create(webrtc::VideoDecoder::kVp9), type, false);
   }
 
   if (type == webrtc::kVideoCodecH264) {
     return AllocatedDecoder(
         webrtc::VideoDecoder::Create(webrtc::VideoDecoder::kH264), type, false);
   }
 
-  // This shouldn't happen, we should not be trying to create something we don't
-  // support.
-  RTC_DCHECK(false);
-  return AllocatedDecoder(NULL, webrtc::kVideoCodecUnknown, false);
+  return AllocatedDecoder(
+      webrtc::VideoDecoder::Create(webrtc::VideoDecoder::kUnsupportedCodec),
+      webrtc::kVideoCodecUnknown, false);
 }
 
 void WebRtcVideoChannel2::WebRtcVideoReceiveStream::ConfigureCodecs(
     const std::vector<VideoCodecSettings>& recv_codecs,
     std::vector<AllocatedDecoder>* old_decoders) {
   *old_decoders = allocated_decoders_;
   allocated_decoders_.clear();
   config_.decoders.clear();
   for (size_t i = 0; i < recv_codecs.size(); ++i) {
     AllocatedDecoder allocated_decoder =
@@ skipping 310 matching lines @@
       video_codecs[i].rtx_payload_type = rtx_mapping[video_codecs[i].codec.id];
     }
   }
 
   return video_codecs;
 }
 
 }  // namespace cricket
 
 #endif  // HAVE_WEBRTC_VIDEO