Improve memory estimate of SpdySessionPool in net/ MemoryDumpProvider.

net/spdy/spdy_header_block.cc

Index: net/spdy/spdy_header_block.cc
diff --git a/net/spdy/spdy_header_block.cc b/net/spdy/spdy_header_block.cc
index 6cbd6ba645c4585a3126099322effb3f9525c968..9fb62a9c1ea3058b88d0f38e37fee6fd76082f51 100644
--- a/net/spdy/spdy_header_block.cc
+++ b/net/spdy/spdy_header_block.cc
@@ -299,6 +299,10 @@ void SpdyHeaderBlock::AppendValueOrAddHeader(const StringPiece key,
   iter->second.Append(GetStorage()->Write(value));
 }
 
+size_t SpdyHeaderBlock::EstimateMemoryUsage() const {
+  return bytes_allocated();
+}
+
 void SpdyHeaderBlock::AppendHeader(const StringPiece key,
                                    const StringPiece value) {
   auto storage = GetStorage();