Adding extra options to interact with external encoder/decoder.

Review URL: https://webrtc-codereview.appspot.com/1327006

git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@3893 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/common_types.h b/common_types.h
index 7b76a39..fd0d1d9 100644
--- a/common_types.h
+++ b/common_types.h
@@ -534,6 +534,11 @@
   kScreensharing
 };
 
+// When using an external encoder/decoder one may need to specify extra
+// options. This struct definition is left for the external implementation.
+// TODO(andresp): Support for multiple external encoder/decoders.
+struct ExtraCodecOptions;
+
 // Common video codec properties
 struct VideoCodec
 {
@@ -556,6 +561,7 @@
     SimulcastStream     simulcastStream[kMaxSimulcastStreams];
 
     VideoCodecMode      mode;
+    ExtraCodecOptions*  extra_options;
 };
 
 // Bandwidth over-use detector options.  These are used to drive