Add overhead per packet observer to the rtp_sender.

webrtc/modules/rtp_rtcp/include/rtp_rtcp.h

 /*
  *  Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #ifndef WEBRTC_MODULES_RTP_RTCP_INCLUDE_RTP_RTCP_H_
 #define WEBRTC_MODULES_RTP_RTCP_INCLUDE_RTP_RTCP_H_
 
 #include <set>
 #include <string>
 #include <utility>
 #include <vector>
 
 #include "webrtc/base/constructormagic.h"
 #include "webrtc/base/deprecation.h"
 #include "webrtc/base/optional.h"
 #include "webrtc/modules/include/module.h"
 #include "webrtc/modules/rtp_rtcp/include/flexfec_sender.h"
 #include "webrtc/modules/rtp_rtcp/include/rtp_rtcp_defines.h"
 #include "webrtc/modules/video_coding/include/video_coding_defines.h"
 
 namespace webrtc {
 
 // Forward declarations.
+class OverheadObserver;
 class RateLimiter;
 class ReceiveStatistics;
 class RemoteBitrateEstimator;
 class RtcEventLog;
 class RtpReceiver;
 class Transport;
 
 RTPExtensionType StringToRtpExtensionType(const std::string& extension);
 
 namespace rtcp {
@@ skipping 42 matching lines @@
     FlexfecSender* flexfec_sender = nullptr;
 
     TransportSequenceNumberAllocator* transport_sequence_number_allocator =
         nullptr;
     BitrateStatisticsObserver* send_bitrate_observer = nullptr;
     FrameCountObserver* send_frame_count_observer = nullptr;
     SendSideDelayObserver* send_side_delay_observer = nullptr;
     RtcEventLog* event_log = nullptr;
     SendPacketObserver* send_packet_observer = nullptr;
     RateLimiter* retransmission_rate_limiter = nullptr;
+    OverheadObserver* overhead_observer = nullptr;
 
    private:
     RTC_DISALLOW_COPY_AND_ASSIGN(Configuration);
   };
 
   // Create a RTP/RTCP module object using the system clock.
   // |configuration|  - Configuration of the RTP/RTCP module.
   static RtpRtcp* CreateRtpRtcp(const RtpRtcp::Configuration& configuration);
 
   // **************************************************************************
@@ skipping 373 matching lines @@
   virtual int32_t SetKeyFrameRequestMethod(KeyFrameRequestMethod method) = 0;
 
   // Sends a request for a keyframe.
   // Returns -1 on failure else 0.
   virtual int32_t RequestKeyFrame() = 0;
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_RTP_RTCP_INCLUDE_RTP_RTCP_H_