Use 'windows' and not 'win32' as the path for the dart testing binary

tools/run_pub.py

 #!/usr/bin/env python
 # Copyright (c) 2015, 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.
 """Used to run pub before the SDK has been built"""
 
 import argparse
 import os
 import platform
 import subprocess
@@ skipping 11 matching lines @@
   result = argparse.ArgumentParser(usage=usage)
   result.add_argument("--package-root", help="package root", default=None)
   result.add_argument("--dart-executable", help="dart binary", default=None)
   return result
 
 def ProcessOptions(options, args):
   return ((options.package_root != None) and
           (options.dart_executable != None))
 
 def GetPrebuiltDartExecutablePath():
-  osdict = {'Darwin':'macos', 'Linux':'linux', 'Windows':'win32'}
+  osdict = {'Darwin':'macos', 'Linux':'linux', 'Windows':'windows'}
   system = platform.system()
   executable_name = 'dart'
   if system == 'Windows':
     executable_name = 'dart.exe'
   try:
     osname = osdict[system]
   except KeyError:
     print >>sys.stderr, ('WARNING: platform "%s" not supported') % (system)
     return None;
   return os.path.join(DART_ROOT,
@@ skipping 38 matching lines @@
     dart_executable = options.dart_executable
   # If requested, use the bootstrap binary instead of the prebuilt
   # executable.
   if os.getenv('DART_USE_BOOTSTRAP_BIN') != None:
     dart_executable = options.dart_executable
   return RunPub(dart_executable, options.package_root, args)
 
 
 if __name__ == '__main__':
   sys.exit(main());