Fix _CheckFilePermissions to actually flag presubmit errors

PRESUBMIT.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.
 
 """Top-level presubmit script for Chromium.
 
 See http://dev.chromium.org/developers/how-tos/depottools/presubmit-scripts
 for more details about the presubmit API built into gcl.
 """
 
 
 import re
-import subprocess
 import sys
 
 
 _EXCLUDED_PATHS = (
     r"^breakpad[\\\/].*",
     r"^native_client_sdk[\\\/]src[\\\/]build_tools[\\\/]make_rules.py",
     r"^native_client_sdk[\\\/]src[\\\/]build_tools[\\\/]make_simple.py",
     r"^native_client_sdk[\\\/]src[\\\/]tools[\\\/].*.mk",
     r"^net[\\\/]tools[\\\/]spdyshark[\\\/].*",
     r"^skia[\\\/].*",
@@ skipping 495 matching lines @@
         warning_descriptions))
   return results
 
 
 def _CheckFilePermissions(input_api, output_api):
   """Check that all files have their permissions properly set."""
   args = [sys.executable, 'tools/checkperms/checkperms.py', '--root',
           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):
   """Makes sure we don't include ui/aura/window_property.h
   in header files.
   """
   pattern = input_api.re.compile(r'^#include\s*"ui/aura/window_property.h"')
   errors = []
   for f in input_api.AffectedFiles():
     if not f.LocalPath().endswith('.h'):
@@ skipping 910 matching lines @@
     trybots.extend(GetDefaultTryConfigs(['cros_x86']))
 
   # The AOSP bot doesn't build the chrome/ layer, so ignore any changes to it
   # unless they're .gyp(i) files as changes to those files can break the gyp
   # step on that bot.
   if (not all(re.search('^chrome', f) for f in files) or
       any(re.search('\.gypi?$', f) for f in files)):
     trybots.extend(GetDefaultTryConfigs(['android_aosp']))
 
   return trybots