Treat policy-disallowed sync xhr as a network error

Bug: 661283

Change-Id: I311cef40e03a264ca9db601842477d502e7cf12d
Reviewed-on: https://chromium-review.googlesource.com/804057
Reviewed-by: Takeshi Yoshino <tyoshino@chromium.org>
Reviewed-by: Rick Byers <rbyers@chromium.org>
Commit-Queue: Ian Clelland <iclelland@chromium.org>
Cr-Commit-Position: refs/heads/master@{#529775}
4 files changed