Undelete the factory method for BackForwardMenuModelGtk.
Undelete the factory method for BackForwardMenuModelGtk.

It's still used by the unit test.

TBR=erg

Review URL: http://codereview.chromium.org/115791

git-svn-id: http://src.chromium.org/svn/trunk/src@16904 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: eb84ea5287f13243be34db2793a9098625eb8239
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser