Add the tree check there instead of implementing it in the root PRESUBMIT.py.

PRESUBMIT.py

 #!/usr/bin/python
 # Copyright (c) 2009 The Chromium Authors. 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 Chromium.
 
 See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts for
 details on the presubmit API built into gcl.
 """
@@ skipping 22 matching lines @@
   try:
     contents = fo.read()
   finally:
     fo.close()
   return contents
 
 
 def CheckChangeOnUpload(input_api, output_api):
   # TODO(maruel): max_cols is temporarily disabled. Reenable once the source
   # tree is in better shape.
-  return (LocalChecks(input_api, output_api, max_cols=0) +
-      input_api.canned_checks.CheckChangeHasBugField(input_api, output_api) +
-      input_api.canned_checks.CheckChangeHasTestField(input_api, output_api))
+  results = []
+  results.extend(LocalChecks(input_api, output_api, max_cols=0))
+  results.extend(input_api.canned_checks.CheckChangeHasBugField(input_api,
+                                                                output_api))
+  results.extend(input_api.canned_checks.CheckChangeHasTestField(input_api,
+                                                                 output_api))
+  return results
 
 
 def CheckChangeOnCommit(input_api, output_api):
+  results = []
   # TODO(maruel): max_cols is temporarily disabled. Reenable once the source
   # tree is in better shape.
-  return (LocalChecks(input_api, output_api, max_cols=0) +
-      input_api.canned_checks.CheckDoNotSubmit(input_api, output_api) +
-      input_api.canned_checks.CheckChangeHasBugField(input_api, output_api) +
-      input_api.canned_checks.CheckChangeHasTestField(input_api, output_api))
+  results.extend(LocalChecks(input_api, output_api, max_cols=0))
+  results.extend(input_api.canned_checks.CheckChangeHasBugField(input_api,
+                                                                output_api))
+  results.extend(input_api.canned_checks.CheckChangeHasTestField(input_api,
+                                                                 output_api))
+  # Make sure the tree is 'open'.
+  results.extend(input_api.canned_checks.CheckTreeIsOpen(
+      input_api, output_api,
+      'http://chromium-status.appspot.com/status', '0'
+  ))
+  return results
 
 
 def LocalChecks(input_api, output_api, max_cols=80):
   """Reports an error if for any source file in SOURCE_FILE_EXTENSIONS:
      - uses CR (or CRLF)
      - contains a TAB
      - has a line that ends with whitespace
      - contains a line >|max_cols| cols unless |max_cols| is 0.
      - File does not end in a newline, or ends in more than one.
 
@@ skipping 63 matching lines @@
 
   if cr_files:
     results.append(output_api.PresubmitError(
         'Found CR (or CRLF) line ending in these files, please use only LF:',
         items=cr_files))
   if eof_files:
     results.append(output_api.PresubmitError(
         'These files should end in one (and only one) newline character:',
         items=eof_files))
   return results