Skip insecure content checks when the frame tree root is remote.

Returning false breaks subframe loads for OOPI bootstrapping.
Temporarily always allow this case to allow forward progress.

BUG=346764

Review URL: https://codereview.chromium.org/342083003

git-svn-id: svn://svn.chromium.org/blink/trunk@176951 bbb929c8-8fbe-4397-9dbb-9b2b20218538