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

base/trace_event/trace_event_argument.cc

 // Copyright (c) 2014 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_argument.h"
 
 #include "base/json/json_writer.h"
 #include "base/values.h"
 
 namespace base {
@@ skipping 90 matching lines @@
 ListValue* TracedValue::GetCurrentArray() {
   DCHECK(!stack_.empty());
   ListValue* list = NULL;
   stack_.back()->GetAsList(&list);
   DCHECK(list);
   return list;
 }
 
 void TracedValue::AppendAsTraceFormat(std::string* out) const {
   std::string tmp;
-  JSONWriter::Write(stack_.front(), &tmp);
+  JSONWriter::Write(*stack_.front(), &tmp);
   *out += tmp;
   DCHECK_EQ(1u, stack_.size()) << tmp;
 }
 
 }  // namespace trace_event
 }  // namespace base