Split the dart_sdk bot script into two runs, one with only apidocs.

tools/bots/dart_sdk.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.
 
 import os
 import os.path
 import shutil
 import sys
@@ skipping 206 matching lines @@
     local_sha256 = bot_utils.CreateSha256ChecksumFile(local_path,
                                                       mangled_filename)
     gsutil.upload(local_sha256, remote_path + '.sha256sum', public=True)
 
 def Run(command, env=None):
   print "Running %s" % ' '.join(command)
   print "Environment %s" % env
   return bot.RunProcess(command, env=env)
 
 if __name__ == '__main__':
-  # We always clobber the bot, to make sure releases are build from scratch
-  force = CHANNEL != bot_utils.Channel.BLEEDING_EDGE
-  bot.Clobber(force=force)
+  if len(sys.argv) > 1 and sys.argv[2] == 'api_docs':
+    if BUILD_OS == 'linux':
+      CreateUploadAPIDocs()
+  else:
+    # We always clobber the bot, to make sure releases are build from scratch
+    force = CHANNEL != bot_utils.Channel.BLEEDING_EDGE
+    bot.Clobber(force=force)
 
-  CreateUploadSDK()
-  if BUILD_OS == 'linux':
-    CreateUploadVersionFile()
-    CreateUploadAPIDocs()
+    CreateUploadSDK()
+    if BUILD_OS == 'linux':
+      CreateUploadVersionFile()