Add more tracing for key frames.

R=mallinath@webrtc.org, stefan@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/1428004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@4015 4adac7df-926f-26a2-2b94-8c16560cd09d

webrtc/modules/rtp_rtcp/source/rtcp_receiver.cc

@@ -918,6 +918,8 @@ void RTCPReceiver::HandlePLI(RTCPUtility::RTCPParserV2& rtcpParser,
                              RTCPPacketInformation& rtcpPacketInformation) {
   const RTCPUtility::RTCPPacket& rtcpPacket = rtcpParser.Packet();
   if (_SSRC == rtcpPacket.PLI.MediaSSRC) {
+    TRACE_EVENT_INSTANT0("webrtc_rtp", "PLI");
+
     // Received a signal that we need to send a new key frame.
     rtcpPacketInformation.rtcpPacketTypeFlags |= kRtcpPli;
   }