CrossSiteResourceHandler: cancel request if there's no RFH to do
a policy check against.

Also included is a new test which demonstrates the issue. This was based
on CrossSiteTransferTest, which I did some cleanup on.

BUG=538784,268640
TEST=content_browsertests, with and without --enable-browser-side-navigation

Review URL: https://codereview.chromium.org/1384113002

Cr-Commit-Position: refs/heads/master@{#352413}
5 files changed