Don't save history state for frames that were initially blocked due to mixed content.

BUG=348952
TEST=Added a dumpBackForwardList() to http/tests/security/mixedContent/insecure-iframe-in-main-frame.html

Review URL: https://codereview.chromium.org/278133002

git-svn-id: svn://svn.chromium.org/blink/trunk@173812 bbb929c8-8fbe-4397-9dbb-9b2b20218538