Ensure iframe navgations are properly constructed in the history tree

If an iframe's first real navigation does not trigger the
HistoryController::updateForInitialLoadInChildFrame() case, the history tree's
cloneAndReplace() will incorrect skip over that frame.

I haven't seen a sample of this outside of pushState() usage in the webui.

BUG=323077

Review URL: https://codereview.chromium.org/84503003

git-svn-id: svn://svn.chromium.org/blink/trunk@163299 bbb929c8-8fbe-4397-9dbb-9b2b20218538