Change presubmit script to not allow uploads at all

PRESUBMIT.py

 # 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.
 
 """Top-level presubmit script for Dart.
 
 See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
 for more details about the presubmit API built into gcl.
 """
 
+MOVED_TO_GITHUB = ("The dart svn repo is no more, and is only here for a "
+    "grace period until dependent projects have moved off. The new repo "
+    "is located at https://github.com/dart-lang/sdk, alongside the rest "
+    "of the dart-lang repos. Commits to this repo will have no effect "
+    "and you should not do it.")
+
 def CheckChangeOnCommit(input_api, output_api):
-  results = []
-  status_check = input_api.canned_checks.CheckTreeIsOpen(
-      input_api,
-      output_api,
-      json_url='http://dart-status.appspot.com/current?format=json')
-  results.extend(status_check)
-  return results
+  return [output_api.PresubmitError(MOVED_TO_GITHUB)]
+
+def CheckChangeOnUpload(input_api, output_api):
+  return [output_api.PresubmitError(MOVED_TO_GITHUB)]
+