Improve memory estimate of SpdySessionPool in net/ MemoryDumpProvider.

net/http2/hpack/decoder/hpack_decoder_string_buffer.cc

Index: net/http2/hpack/decoder/hpack_decoder_string_buffer.cc
diff --git a/net/http2/hpack/decoder/hpack_decoder_string_buffer.cc b/net/http2/hpack/decoder/hpack_decoder_string_buffer.cc
index e38f42db9773a012ea0abe438c01ccebcba061b3..e00c155b435b2a53de8919bbcf8f5f883c09e44c 100644
--- a/net/http2/hpack/decoder/hpack_decoder_string_buffer.cc
+++ b/net/http2/hpack/decoder/hpack_decoder_string_buffer.cc
@@ -7,6 +7,7 @@
 #include <utility>
 
 #include "base/logging.h"
+#include "base/trace_event/memory_usage_estimator.h"
 #include "net/http2/tools/http2_bug_tracker.h"
 
 using base::StringPiece;
@@ -224,6 +225,10 @@ void HpackDecoderStringBuffer::OutputDebugStringTo(std::ostream& out) const {
   out << "}";
 }
 
+size_t HpackDecoderStringBuffer::EstimateMemoryUsage() const {
+  return base::trace_event::EstimateMemoryUsage(buffer_);
+}
+
 std::ostream& operator<<(std::ostream& out, const HpackDecoderStringBuffer& v) {
   v.OutputDebugStringTo(out);
   return out;