Add logging to the QUIC write path.

net/quic/quic_packet_generator.h

Index: net/quic/quic_packet_generator.h
diff --git a/net/quic/quic_packet_generator.h b/net/quic/quic_packet_generator.h
index 9af5d8a4b55b3b652a6d1f7355503ad90e1c2a35..f47a540194aca5e24fd1167df87b1d8ee28818c6 100644
--- a/net/quic/quic_packet_generator.h
+++ b/net/quic/quic_packet_generator.h
@@ -70,7 +70,19 @@ class NET_EXPORT_PRIVATE QuicPacketGenerator {
     virtual bool OnSerializedPacket(const SerializedPacket& packet) = 0;
   };
 
+  // Interface which gets callbacks from the QuicPacketGenerator at interesting
+  // points.  Implementations must not mutate the state of the generator
+  // as a result of these callbacks.
+  class NET_EXPORT_PRIVATE DebugDelegateInterface {
+   public:
+    virtual ~DebugDelegateInterface() {}
+
+    // Called when a frame has been added to the current packet.
+    virtual void OnFrameAddedToPacket(const QuicFrame& frame) = 0;
+  };
+
   QuicPacketGenerator(DelegateInterface* delegate,
+                      DebugDelegateInterface* debug_delegate,
                       QuicPacketCreator* creator);
 
   virtual ~QuicPacketGenerator();
@@ -89,14 +101,21 @@ class NET_EXPORT_PRIVATE QuicPacketGenerator {
 
   bool HasQueuedFrames() const;
 
+  void set_debug_delegate(DebugDelegateInterface* debug_delegate) {
+    debug_delegate_ = debug_delegate;
+  }
+
  private:
   void SendQueuedFrames();
 
   bool HasPendingFrames() const;
   bool AddNextPendingFrame();
+
+  bool AddFrame(const QuicFrame& frame);
   void SerializeAndSendPacket();
 
   DelegateInterface* delegate_;
+  DebugDelegateInterface* debug_delegate_;
 
   QuicPacketCreator* packet_creator_;
   QuicFrames queued_control_frames_;