Fix _CheckFilePermissions to actually flag presubmit errors

PRESUBMIT.py

Index: PRESUBMIT.py
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index 4a7e384c3c01d52dd7e491b17192ec1ec8e0bd62..e0e104005f94da26a315017ae63e3061998b0578 100644
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -526,14 +526,12 @@ def _CheckFilePermissions(input_api, output_api):
           input_api.change.RepositoryRoot()]
   for f in input_api.AffectedFiles():
     args += ['--file', f.LocalPath()]
-  errors = []
-  (errors, stderrdata) = subprocess.Popen(args).communicate()
-
-  results = []
+  checkperms = subprocess.Popen(args, stdout=subprocess.PIPE)

[M-A Ruel, 2014/01/29 21:28:19]

What you want is
errors = input_api.subprocess.check_output(args)

unless checkperms.py normally return non-zero.

[adamk, 2014/01/29 21:39:54]

Not sure what you mean by "normally", but it returns non-zero when there are bad
permissions, so it seems like check_output's not a good match here.

[M-A Ruel, 2014/01/29 21:47:05]

Normally would be in absence of catastrophic failure. Still, do not add
reference to global subprocess import, it was unwarranted. Use
input_api.subprocess instead.

[adamk, 2014/01/29 21:52:54]

Ok, will do, but note that I didn't add this reference, it was here already.

+  errors = checkperms.communicate()[0].strip()
   if errors:
-    results.append(output_api.PresubmitError('checkperms.py failed.',
-                                             errors))
-  return results
+    return [output_api.PresubmitError('checkperms.py failed.',
+                                      errors.splitlines())]
+  return []
 
 
 def _CheckNoAuraWindowPropertyHInHeaders(input_api, output_api):