Add clang-format to presubmit checks

The check doesn't modify the patch, instead, you'll have to use "git cl
format" manually.

BUG=none
R=danno@google.com, danno@chromium.org, jkummerow@chromium.org
LOG=y

Review URL: https://codereview.chromium.org/362263002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22165 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

PRESUBMIT.py

@@ -114,6 +114,8 @@ def _CommonChecks(input_api, output_api):
   results = []
   results.extend(input_api.canned_checks.CheckOwners(
       input_api, output_api, source_file_filter=None))
+  results.extend(input_api.canned_checks.CheckPatchFormatted(
+      input_api, output_api))
   results.extend(_V8PresubmitChecks(input_api, output_api))
   results.extend(_CheckUnwantedDependencies(input_api, output_api))
   return results