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

webrtc/common_types.h

Index: webrtc/common_types.h
diff --git a/webrtc/common_types.h b/webrtc/common_types.h
index 048485fa2fc89f99483230cb2f0b5f479acb7ed0..50804293f735fbd96153d6ee227007d90b080afd 100644
--- a/webrtc/common_types.h
+++ b/webrtc/common_types.h
@@ -281,6 +281,15 @@ class SendSideDelayObserver {
                                     uint32_t ssrc) = 0;
 };
 
+// Callback, used to notify an observer whenever a packet is sent to network.

[stefan-webrtc, 2016/01/18 19:48:25]

Maybe "sent to the transport" since this is when the packet leaves the webrtc
layer and not when it leaves the socket.

[åsapersson, 2016/04/06 14:52:37]

Done.

+class SendPacketObserver {
+ public:
+  virtual ~SendPacketObserver() {}
+  virtual void OnSendPacket(uint16_t packet_id,
+                            int64_t capture_time_ms,
+                            uint32_t ssrc) = 0;
+};
+
 // ==================================================================
 // Voice specific types
 // ==================================================================