Add a canned clang-format presubmit check

presubmit_canned_checks.py

Index: presubmit_canned_checks.py
diff --git a/presubmit_canned_checks.py b/presubmit_canned_checks.py
index b11102a94332c8e727dbeccb8b5b44c69563d723..d52ad9582df3a2c2e81809054a903f0754694ca6 100644
--- a/presubmit_canned_checks.py
+++ b/presubmit_canned_checks.py
@@ -1041,3 +1041,15 @@ def PanProjectChecks(input_api, output_api,
         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)

[iannucci, 2014/01/17 20:28:50]

kinda unfortunate that we throw away the results... how long does this take to
run?

[enne (OOO), 2014/01/17 21:26:12]

If you had results, what would you do with them? Do you want to stick the output
in /tmp somewhere and give a command that folks can apply rather than just
rerunning git cl format?


In terms of time, for this example patch:
https://codereview.chromium.org/139053002/

enne@tropy:/work/src$ time git cl format

real	0m1.040s
user	0m0.790s
sys	0m0.120s

This is about the same for git cl format --full that formats the whole file.

It definitely does take longer on patches that touch more files.  On a patch
that had about 1800 files changed, it was more in the ballpark of 15 seconds.

+  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 []