Improve memory estimate of SpdySessionPool in net/ MemoryDumpProvider.

net/spdy/hpack/hpack_decoder3.cc

Index: net/spdy/hpack/hpack_decoder3.cc
diff --git a/net/spdy/hpack/hpack_decoder3.cc b/net/spdy/hpack/hpack_decoder3.cc
index 5c6fbb8bc907ed6b4dfc4a45710169fe5c30f72c..eb559b0d9e0d6a5e6c6e46d82ebb87e2b3f91f9c 100644
--- a/net/spdy/hpack/hpack_decoder3.cc
+++ b/net/spdy/hpack/hpack_decoder3.cc
@@ -5,6 +5,7 @@
 #include "net/spdy/hpack/hpack_decoder3.h"
 
 #include "base/logging.h"
+#include "base/trace_event/memory_usage_estimator.h"
 #include "net/http2/decoder/decode_buffer.h"
 #include "net/http2/decoder/decode_status.h"
 
@@ -107,6 +108,10 @@ void HpackDecoder3::set_max_decode_buffer_size_bytes(
   hpack_decoder_.set_max_string_size_bytes(max_decode_buffer_size_bytes);
 }
 
+size_t HpackDecoder3::EstimateMemoryUsage() const {
+  return base::trace_event::EstimateMemoryUsage(hpack_decoder_);
+}
+
 HpackDecoder3::ListenerAdapter::ListenerAdapter() : handler_(nullptr) {}
 HpackDecoder3::ListenerAdapter::~ListenerAdapter() {}