Add OS::GetCurrentProcessId and prepend output from trace-gc with the current pid

src/v8utils.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 39 matching lines @@
 #endif
 #else
 #define PRINTF_CHECKING
 #define FPRINTF_CHECKING
 #endif
 
 // Our version of printf().
 void PRINTF_CHECKING PrintF(const char* format, ...);
 void FPRINTF_CHECKING PrintF(FILE* out, const char* format, ...);
 
+// Prepredings the current process ID to the output.
+void PRINTF_CHECKING PrintPID(const char* format, ...);
+
 // Our version of fflush.
 void Flush(FILE* out);
 
 inline void Flush() {
   Flush(stdout);
 }
 
 
 // Read a line of characters after printing the prompt to stdout. The resulting
 // char* needs to be disposed off with DeleteArray by the caller.
@@ skipping 200 matching lines @@
 
   // Add formatted contents like printf based on a va_list.
   void AddFormattedList(const char* format, va_list list);
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(StringBuilder);
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_V8UTILS_H_