use more distinctive pattern to mark where dart source goes

runtime/tools/create_string_literal.py

 # Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 #
 # This python script creates a string literal in a C++ source file from a C++
 # source template and text file.
 
 import os
 import sys
 from os.path import join
@@ skipping 15 matching lines @@
           result += '\n   '
           lineCounter = 0
       if lineCounter != 0:
         result += '\n   '
   result += ' // Terminating null character.\n    0'
   return result
 
 
 def makeFile(output_file, input_cc_file, input_files):
   bootstrap_cc_text = open(input_cc_file).read()
-  bootstrap_cc_text = bootstrap_cc_text % makeString(input_files)
+  bootstrap_cc_text = bootstrap_cc_text.replace("{{DART_SOURCE}}",
+      makeString(input_files))
   open(output_file, 'w').write(bootstrap_cc_text)
   return True
 
 
 def main(args):
   try:
     # Parse input.
     parser = OptionParser()
     parser.add_option("--output",
                       action="store", type="string",
@@ skipping 22 matching lines @@
 
     return 0
   except Exception, inst:
     sys.stderr.write('create_string_literal.py exception\n')
     sys.stderr.write(str(inst))
     sys.stderr.write('\n')
     return -1
 
 if __name__ == '__main__':
   sys.exit(main(sys.argv))