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..8ba9224520435ded152f43ef7da5a96f6ee29cf1 100644
--- a/net/spdy/hpack/hpack_decoder3.cc
+++ b/net/spdy/hpack/hpack_decoder3.cc
@@ -107,6 +107,10 @@ 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 hpack_decoder_.EstimateMemoryUsage();
+}
+
 HpackDecoder3::ListenerAdapter::ListenerAdapter() : handler_(nullptr) {}
 HpackDecoder3::ListenerAdapter::~ListenerAdapter() {}