Remove webrtc::kVideoCodecUnknown.

It's being removed from WebRTC in favour of kVideoCodecGeneric.

Bug: webrtc:8136
Change-Id: I74cb60cbfee56320bd40bf0bfc31887fe0dac05d
Reviewed-on: https://chromium-review.googlesource.com/1186337
Commit-Queue: Olga Sharonova <olka@chromium.org>
Reviewed-by: Olga Sharonova <olka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585447}

content/renderer/media/webrtc/rtc_video_encoder.cc

@@ -63,7 +63,7 @@ webrtc::VideoCodecType ProfileToWebRtcVideoCodecType(
     return webrtc::kVideoCodecH264;
   }
   NOTREACHED() << "Invalid profile " << GetProfileName(profile);
-  return webrtc::kVideoCodecUnknown;
+  return webrtc::kVideoCodecGeneric;
 }
 
 // Populates struct webrtc::RTPFragmentationHeader for H264 codec.