Improve memory estimate of SpdySessionPool in net/ MemoryDumpProvider.

net/http2/hpack/decoder/hpack_decoder_string_buffer.h

Index: net/http2/hpack/decoder/hpack_decoder_string_buffer.h
diff --git a/net/http2/hpack/decoder/hpack_decoder_string_buffer.h b/net/http2/hpack/decoder/hpack_decoder_string_buffer.h
index 85449415860096c9ed73b1ff4c310df1a6e5587b..2f60068e608bc57b34f99fe395523dc6e8c098ed 100644
--- a/net/http2/hpack/decoder/hpack_decoder_string_buffer.h
+++ b/net/http2/hpack/decoder/hpack_decoder_string_buffer.h
@@ -62,6 +62,9 @@ class NET_EXPORT_PRIVATE HpackDecoderStringBuffer {
   Backing backing_for_testing() const { return backing_; }
   void OutputDebugStringTo(std::ostream& out) const;
 
+  // Returns the estimate of dynamically allocated memory in bytes.
+  size_t EstimateMemoryUsage() const;
+
  private:
   // Storage for the string being buffered, if buffering is necessary
   // (e.g. if Huffman encoded, buffer_ is storage for the decoded string).