HPACK optimal Huffman code instrumentation and UMA collection.

net/spdy/hpack_encoder.cc

Index: net/spdy/hpack_encoder.cc
diff --git a/net/spdy/hpack_encoder.cc b/net/spdy/hpack_encoder.cc
index 469042687718e25f7a23e689e1fb900688123818..d037fa837557199c1ee188da417042de8af65a4c 100644
--- a/net/spdy/hpack_encoder.cc
+++ b/net/spdy/hpack_encoder.cc
@@ -13,7 +13,10 @@ using base::StringPiece;
 using std::string;
 
 HpackEncoder::HpackEncoder()
-    : max_string_literal_size_(kDefaultMaxStringLiteralSize) {}
+    : max_string_literal_size_(kDefaultMaxStringLiteralSize),
+      char_counts_(NULL),
+      total_char_counts_(NULL) {
+}
 
 HpackEncoder::~HpackEncoder() {}
 
@@ -38,11 +41,20 @@ bool HpackEncoder::EncodeHeaderSet(const std::map<string, string>& header_set,
         it->first, it->second)) {
       return false;
     }
+    UpdateCharacterCounts(it->first);
+    UpdateCharacterCounts(it->second);
   }
   output_stream.TakeString(output);
   return true;
 }
 
+void HpackEncoder::SetCharCountsStorage(std::vector<size_t>* char_counts,
+                                        size_t* total_char_counts) {
+  CHECK_LE(256u, char_counts->size());
+  char_counts_ = char_counts;
+  total_char_counts_ = total_char_counts;
+}
+
 void HpackEncoder::CookieToCrumbs(StringPiece cookie,
                                   std::vector<StringPiece>* out) {
   out->clear();
@@ -63,4 +75,14 @@ void HpackEncoder::CookieToCrumbs(StringPiece cookie,
   }
 }
 
+void HpackEncoder::UpdateCharacterCounts(base::StringPiece str) {
+  if (char_counts_ == NULL || total_char_counts_ == NULL) {
+    return;
+  }
+  for (StringPiece::const_iterator it = str.begin(); it != str.end(); ++it) {
+    ++(*char_counts_)[static_cast<uint8>(*it)];
+  }
+  (*total_char_counts_) += str.size();
+}
+
 }  // namespace net