Add annotated steps for src tarball creation bot

tools/bots/bot.py

 #!/usr/bin/python
 
 # Copyright (c) 2012, 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.
 
 """
 Shared code for use in the buildbot scripts.
 """
 
@@ skipping 133 matching lines @@
     sys.exit(1)
 
   # Print out the buildinfo for easy debugging.
   build_info.PrintBuildInfo()
 
   # Make sure we are in the dart directory
   os.chdir(DART_PATH)
 
   try:
     Clobber()
-    build_step(build_info)
+    if build_step: 
+      build_step(build_info)
 
     custom_steps(build_info)
   except OSError as e:
     sys.exit(e.errno)
 
   sys.exit(0)
 
 
 def GetBotName():
   """
@@ skipping 81 matching lines @@
   if exit_code != 0:
     raise OSError(exit_code)
 
 
 def GetStepName(name, flags):
   """
   Filters out flags with '=' as this breaks the /stats feature of the buildbot.
   """
   flags = [x for x in flags if not '=' in x]
   return ('%s tests %s' % (name, ' '.join(flags))).strip()