Reduce flakiness of browser tests.

tools/testing/perf_testing/create_graph.py

 #!/usr/bin/python
 
 # 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.
 
 import datetime
 import math
 from matplotlib.font_manager import FontProperties
 import matplotlib.pyplot as plt
@@ skipping 50 matching lines @@
        stdout to 
     append: True if we want to append to the file instead of overwriting it"""
   if VERBOSE:
     print ' '.join(cmd_list)
   out = subprocess.PIPE
   if outfile:
     mode = 'w'
     if append:
       mode = 'a'
     out = open(outfile, mode)
+    if append:
+      # Annoying Windows "feature" -- append doesn't actually append unless you 
+      # explicitly go to the end of the file.
+      # http://mail.python.org/pipermail/python-list/2009-October/1221859.html
+      out.seek(0, os.SEEK_END)
   p = subprocess.Popen(cmd_list, stdout = out, stderr = subprocess.PIPE,
       shell=HAS_SHELL)
   output, not_used = p.communicate();
   if output:
     print output
   return output
 
 def time_cmd(cmd):
   """Determine the amount of (real) time it takes to execute a given command."""
   start = time.time()
@@ skipping 664 matching lines @@
       if has_new_code():
         run_test_sequence(cl, size, language, perf)
       else:
         time.sleep(SLEEP_TIME)
   else:
     run_test_sequence(cl, size, language, perf)
 
 if __name__ == '__main__':
   main()