Fix _CheckFilePermissions to actually flag presubmit errors

Previously it was misusing subprocess.Popen such that no output
was ever captured from checkperms.py.

Also, changed the check to use input_api.subprocess instead of importing subprocess.

[email protected]
NOTRY=true

Review URL: https://codereview.chromium.org/143013004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247805 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index d19fa7f7..2e6c077 100644
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -10,7 +10,6 @@
 
 
 import re
-import subprocess
 import sys
 
 
@@ -526,14 +525,13 @@
           input_api.change.RepositoryRoot()]
   for f in input_api.AffectedFiles():
     args += ['--file', f.LocalPath()]
-  errors = []
-  (errors, stderrdata) = subprocess.Popen(args).communicate()
-
-  results = []
+  checkperms = input_api.subprocess.Popen(args,
+                                          stdout=input_api.subprocess.PIPE)
+  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):