Simplify HistoryController logic for updating when a load commits

Back/forward, reload, and client redirects are all sufficiently similar that
they can be merged into a single path.

Also, rename a couple internal HistoryController functions to better describe
when they are used.

BUG=none

Review URL: https://chromiumcodereview.appspot.com/23513069

git-svn-id: svn://svn.chromium.org/blink/trunk@158392 bbb929c8-8fbe-4397-9dbb-9b2b20218538