Keep frames to navigate alive in HistoryController::goToEntry()

Otherwise, if a script executed during the navigation of one frame (for
instance a popstate event handler) removes other frames from the document,
the calls to navigate those frames later on are given pointers to dead
objects.

This patch makes the more localized fix committed as r165081 redundant,
and thus reverts it from FrameLoader::loadHistoryItem().

BUG=337120

Review URL: https://codereview.chromium.org/145493005

git-svn-id: svn://svn.chromium.org/blink/trunk@165724 bbb929c8-8fbe-4397-9dbb-9b2b20218538