Start NACKing as soon as we have the first packet of a key frame.

BUG=1605

Review URL: https://webrtc-codereview.appspot.com/1307007

git-svn-id: http://webrtc.googlecode.com/svn/trunk@3855 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/modules/video_coding/main/source/session_info.cc

@@ -353,6 +353,11 @@ int VCMSessionInfo::MakeDecodable() {
   return return_length;
 }
 
+bool
+VCMSessionInfo::HaveFirstPacket() const {
+  return !packets_.empty() && packets_.front().isFirstPacket;
+}
+
 bool
 VCMSessionInfo::HaveLastPacket() const {
   return (!packets_.empty() && packets_.back().markerBit);