Convert JsonWriter::Write to taking a const ref for the in-param

base/trace_event/trace_event_system_stats_monitor.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/trace_event/trace_event_system_stats_monitor.h"
 
 #include "base/debug/leak_annotations.h"
 #include "base/json/json_writer.h"
 #include "base/lazy_instance.h"
 #include "base/logging.h"
@@ skipping 107 matching lines @@
   dump_timer_.Stop();
 }
 
 bool TraceEventSystemStatsMonitor::IsTimerRunningForTest() const {
   return dump_timer_.IsRunning();
 }
 
 void AppendSystemProfileAsTraceFormat(const SystemMetrics& system_metrics,
                                       std::string* output) {
   std::string tmp;
-  base::JSONWriter::Write(system_metrics.ToValue().get(), &tmp);
+  base::JSONWriter::Write(*system_metrics.ToValue(), &tmp);
   *output += tmp;
 }
 
 }  // namespace trace_event
 }  // namespace base