bot: fix to get appropriate executable in windows.

tools/utils.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 file contains a set of utilities functions used by other Python-based
 # scripts.
 
 import commands
 import os
 import platform
@@ skipping 101 matching lines @@
 # Returns the path to the Dart test runner (executes the .dart file).
 def GetDartRunner(mode, arch, component):
   build_root = GetBuildRoot(GuessOS(), mode, arch)
   if component == 'dartc':
     return os.path.join(build_root, 'compiler', 'bin', 'dartc_test')
   elif component == 'frog':
     return os.path.join(build_root, 'frog', 'bin', 'frog')
   elif component == 'frogsh':
     return os.path.join(build_root, 'frog', 'bin', 'frogsh')
   else:
-    return os.path.join(build_root, 'dart')
+    suffix = ''
+    if IsWindows():
+      suffix = '.exe'
+    return os.path.join(build_root, 'dart') + suffix
 
 
 # Mapping table between build mode and build configuration.
 BUILD_MODES = {
   'debug': 'Debug',
   'release': 'Release',
 }
 
 
 # Mapping table between OS and build output location.
@@ skipping 124 matching lines @@
   def __init__(self, value):
     self.value = value
 
   def __str__(self):
     return repr(self.value)
 
 
 if __name__ == "__main__":
   import sys
   Main(sys.argv)