Improve memory estimate of SpdySessionPool in net/ MemoryDumpProvider.

net/spdy/header_coalescer.cc

Index: net/spdy/header_coalescer.cc
diff --git a/net/spdy/header_coalescer.cc b/net/spdy/header_coalescer.cc
index 24bd9cb7d00ea42ac2239239d681185e31179e10..0aac2babbfd53729aef1331aa558d1a187020846 100644
--- a/net/spdy/header_coalescer.cc
+++ b/net/spdy/header_coalescer.cc
@@ -7,6 +7,7 @@
 #include <utility>
 
 #include "base/strings/string_util.h"
+#include "base/trace_event/memory_usage_estimator.h"
 
 namespace net {
 
@@ -70,4 +71,8 @@ SpdyHeaderBlock HeaderCoalescer::release_headers() {
   return std::move(headers_);
 }
 
+size_t HeaderCoalescer::EstimateMemoryUsage() const {
+  return base::trace_event::EstimateMemoryUsage(headers_);
+}
+
 }  // namespace net