Add trace code to track all posted tasks in message_loop.

base/location.h

 // Copyright (c) 2011 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_LOCATION_H_
 #define BASE_LOCATION_H_
 
 #include <string>
 
 #include "base/base_export.h"
@@ skipping 42 matching lines @@
 
   std::string ToString() const;
 
   void Write(bool display_filename, bool display_function_name,
              std::string* output) const;
 
   // Write function_name_ in HTML with '<' and '>' properly encoded.
   void WriteFunctionName(std::string* output) const;
 
  private:
-  const char* const function_name_;
-  const char* const file_name_;
-  const int line_number_;
-  const void* const program_counter_;
+  const char* function_name_;
+  const char* file_name_;
+  int line_number_;
+  const void* program_counter_;
 };
 
 BASE_EXPORT const void* GetProgramCounter();
 
 // Define a macro to record the current source location.
 #define FROM_HERE tracked_objects::Location(                                   \
     __FUNCTION__,                                                              \
     __FILE__,                                                                  \
     __LINE__,                                                                  \
     tracked_objects::GetProgramCounter())                                      \
 
 }  // namespace tracked_objects
 
 #endif  // BASE_LOCATION_H_