Adding a ToPrettyString method to ConvertableToTracedValue.

base/debug/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_DEBUG_TRACE_EVENT_ARGUMENT_H_
 #define BASE_DEBUG_TRACE_EVENT_ARGUMENT_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 23 matching lines @@
   void BeginArray(const char* name);
 
   void AppendInteger(int);
   void AppendDouble(double);
   void AppendBoolean(bool);
   void AppendString(const std::string&);
   void BeginArray();
   void BeginDictionary();
 
   virtual void AppendAsTraceFormat(std::string* out) const OVERRIDE;
+  virtual std::string ToPrettyString() const OVERRIDE;
 
  private:
   virtual ~TracedValue();
 
   DictionaryValue* GetCurrentDictionary();
   ListValue* GetCurrentArray();
 
   scoped_ptr<base::Value> root_;
   std::vector<Value*> stack_;
   DISALLOW_COPY_AND_ASSIGN(TracedValue);
 };
 
 }  // namespace debug
 }  // namespace base
 
 #endif  // BASE_DEBUG_TRACE_EVENT_ARGUMENT_H_