Add a canned clang-format presubmit check

presubmit_canned_checks.py

 # Copyright (c) 2012 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.
 
 """Generic presubmit checks that can be reused by other presubmit checks."""
 
 import os as _os
 _HERE = _os.path.dirname(_os.path.abspath(__file__))
 
 
@@ skipping 1023 matching lines @@
     snapshot("checking description")
     results.extend(input_api.canned_checks.CheckChangeHasDescription(
         input_api, output_api))
     results.extend(input_api.canned_checks.CheckDoNotSubmitInDescription(
         input_api, output_api))
     snapshot("checking do not submit in files")
     results.extend(input_api.canned_checks.CheckDoNotSubmitInFiles(
         input_api, output_api))
   snapshot("done")
   return results
+
+
+def CheckPatchFormatted(input_api, output_api):
+  import git_cl
+  code, _ = git_cl.RunGitWithCode(['cl', 'format', '--dry-run'],
+                                    suppress_stderr=True)
+  if code == 2:
+    return [output_api.PresubmitPromptWarning(
+      'Your patch is not formatted, please run git cl format.')]
+  # As this is just a warning, ignore all other errors if the user
+  # happens to have a broken clang-format, doesn't use git, etc etc.
+  return []