QUIC - add instrumentation to HPACK.

net/quic/quic_headers_stream.h

Index: net/quic/quic_headers_stream.h
diff --git a/net/quic/quic_headers_stream.h b/net/quic/quic_headers_stream.h
index ffa5ecdd7c563d74f27cde650d9e8184f5dd9cb4..ac78b5daf2862b3662f1a0a9885ca6c5c6ed6050 100644
--- a/net/quic/quic_headers_stream.h
+++ b/net/quic/quic_headers_stream.h
@@ -26,6 +26,21 @@ class QuicSpdySession;
 // to send and receive headers.
 class NET_EXPORT_PRIVATE QuicHeadersStream : public ReliableQuicStream {
  public:
+  class NET_EXPORT_PRIVATE HpackDebugVisitor {
+   public:
+    HpackDebugVisitor();
+
+    virtual ~HpackDebugVisitor();
+
+    // For each HPACK indexed representation processed, |elapsed| is
+    // the time since the corresponding entry was added to the dynamic
+    // table.
+    virtual void OnUseEntry(QuicTime::Delta elapsed) = 0;
+
+   private:
+    DISALLOW_COPY_AND_ASSIGN(HpackDebugVisitor);
+  };
+
   explicit QuicHeadersStream(QuicSpdySession* session);
   ~QuicHeadersStream() override;
 
@@ -56,6 +71,10 @@ class NET_EXPORT_PRIVATE QuicHeadersStream : public ReliableQuicStream {
   // induced HOL blocking in QUIC.
   void DisableHpackDynamicTable();
 
+  // Optional, enables instrumentation related to go/quic-hpack.
+  void SetHpackEncoderDebugVisitor(std::unique_ptr<HpackDebugVisitor> visitor);
+  void SetHpackDecoderDebugVisitor(std::unique_ptr<HpackDebugVisitor> visitor);
+
  private:
   class SpdyFramerVisitor;