Skip _CheckFilePermissions check on Windows

Executable bits are wonky on Windows, so checking them doesn't get us anything
and incorrectly disallows uploading of, e.g., python scripts.

R=maruel@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/142973008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248605 0039d316-1c4b-4281-b951-d872f2087c98
Docserver: Fix cron test broken by requirement of whats_new.json.

BUG=None
TBR=yoz@chromium.org

Review URL: https://codereview.chromium.org/145913003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248606 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248606