HPACK optimal Huffman code instrumentation and UMA collection.

net/spdy/hpack_encoder.h

Index: net/spdy/hpack_encoder.h
diff --git a/net/spdy/hpack_encoder.h b/net/spdy/hpack_encoder.h
index df504f50f83e52c39e1a53ae2fe074a10cc02f5b..ec03af0a5bec0c6578c9ef05c375116674a5a19a 100644
--- a/net/spdy/hpack_encoder.h
+++ b/net/spdy/hpack_encoder.h
@@ -56,6 +56,11 @@ class NET_EXPORT_PRIVATE HpackEncoder {
     header_table_.SetSettingsHeaderTableSize(size_setting);
   }
 
+  // Sets externally-owned storage for aggregating character counts of emitted
+  // literal representations.
+  void SetCharCountsStorage(std::vector<size_t>* char_counts,
+                            size_t* total_char_counts);
+
  private:
   typedef std::pair<base::StringPiece, base::StringPiece> Representation;
   typedef std::vector<Representation> Representations;
@@ -72,6 +77,8 @@ class NET_EXPORT_PRIVATE HpackEncoder {
   // Emits a Huffman or identity string (whichever is smaller).
   void EmitString(base::StringPiece str);
 
+  void UpdateCharacterCounts(base::StringPiece str);
+
   // Determines the representation delta required to encode |header_set| in
   // the current header table context. Entries in the reference set are
   // enumerated and marked with membership in the current |header_set|.
@@ -88,6 +95,10 @@ class NET_EXPORT_PRIVATE HpackEncoder {
   bool allow_huffman_compression_;
   const HpackHuffmanTable& huffman_table_;
 
+  // Externally-owned, nullable storage for character counts of literals.
+  std::vector<size_t>* char_counts_;
+  size_t* total_char_counts_;
+
   DISALLOW_COPY_AND_ASSIGN(HpackEncoder);
 };