Update from https://crrev.com/329939

base/trace_event/trace_event_argument.h

 // Copyright 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.
 
 #ifndef BASE_TRACE_EVENT_TRACE_EVENT_ARGUMENT_H_
 #define BASE_TRACE_EVENT_TRACE_EVENT_ARGUMENT_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 11 matching lines @@
  public:
   TracedValue();
 
   void EndDictionary();
   void EndArray();
 
   void SetInteger(const char* name, int value);
   void SetDouble(const char* name, double);
   void SetBoolean(const char* name, bool value);
   void SetString(const char* name, const std::string& value);
-  void SetValue(const char* name, Value* value);
+  void SetValue(const char* name, scoped_ptr<Value> value);
   void BeginDictionary(const char* name);
   void BeginArray(const char* name);
 
   void AppendInteger(int);
   void AppendDouble(double);
   void AppendBoolean(bool);
   void AppendString(const std::string&);
   void BeginArray();
   void BeginDictionary();
 
   void AppendAsTraceFormat(std::string* out) const override;
 
  private:
   ~TracedValue() override;
 
   DictionaryValue* GetCurrentDictionary();
   ListValue* GetCurrentArray();
 
   scoped_ptr<base::Value> root_;
-  std::vector<Value*> stack_;
+  std::vector<Value*> stack_;  // Weak references.
   DISALLOW_COPY_AND_ASSIGN(TracedValue);
 };
 
 }  // namespace trace_event
 }  // namespace base
 
 #endif  // BASE_TRACE_EVENT_TRACE_EVENT_ARGUMENT_H_