Revert "Split the frame tree logic out of HistoryItem"

This reverts commit 248946a4198984d6e60c2c60b280bf2345c00f47
(http://src.chromium.org/viewvc/blink?revision=162131&view=revision).

This patch caused a bunch of assertions in android webview.

TBR=abarth

git-svn-id: svn://svn.chromium.org/blink/trunk@162144 bbb929c8-8fbe-4397-9dbb-9b2b20218538