Add histogram stats for send delay for a sent video stream.

webrtc/video/vie_channel.h

Index: webrtc/video/vie_channel.h
diff --git a/webrtc/video/vie_channel.h b/webrtc/video/vie_channel.h
index ed0712ba42a3c26c46f13c34a1f085c2525e7298..e13e2c7871b6468bbb05b755391c3723b160b037 100644
--- a/webrtc/video/vie_channel.h
+++ b/webrtc/video/vie_channel.h
@@ -187,6 +187,8 @@ class ViEChannel : public VCMFrameTypeCallback,
 
   void RegisterSendSideDelayObserver(SendSideDelayObserver* observer);
 
+  void RegisterSendPacketObserver(SendPacketObserver* observer);
+
   // Called on any new send bitrate estimate.
   void RegisterSendBitrateObserver(BitrateStatisticsObserver* observer);
 
@@ -304,6 +306,7 @@ class ViEChannel : public VCMFrameTypeCallback,
       BitrateStatisticsObserver* send_bitrate_observer,
       FrameCountObserver* send_frame_count_observer,
       SendSideDelayObserver* send_side_delay_observer,
+      SendPacketObserver* send_packet_observer,
       size_t num_modules);
 
   // Assumed to be protected.
@@ -380,6 +383,17 @@ class ViEChannel : public VCMFrameTypeCallback,
     }
   } send_side_delay_observer_;
 
+  class RegisterableSendPacketObserver
+      : public RegisterableCallback<SendPacketObserver> {
+    void OnSendPacket(uint16_t packet_id,
+                      int64_t capture_time_ms,
+                      uint32_t ssrc) override {
+      CriticalSectionScoped cs(critsect_.get());
+      if (callback_)
+        callback_->OnSendPacket(packet_id, capture_time_ms, ssrc);
+    }
+  } send_packet_observer_;
+
   class RegisterableRtcpPacketTypeCounterObserver
       : public RegisterableCallback<RtcpPacketTypeCounterObserver> {
    public: