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.

R=maruel@chromium.org
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
Fixed chrome://settings/accounts availability for MP.

BUG=230018
TEST=manual tests on Peppy

Review URL: https://codereview.chromium.org/144983002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247806 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247805
SVN changes up to revision 247806