Revert 162460 "Use const Node reference for member functions in ..."

> Use const Node reference for member functions in DocumentMarkerController
> 
> This patch changes Node pointer parameter to const Node reference in member functions in DocumentController because these parameters are never null for ease of maintenance.
> 
> This patch is a part of using const Node reference for Document::did{Insert,Remove,Merge,Split}Text(), http://crrev.com/24023002.
> 
> BUG=n/a
> TEST=n/a; no behavior changes
> 
> Review URL: https://codereview.chromium.org/80273002

TBR=yosin@chromium.org

Review URL: https://codereview.chromium.org/82533002

git-svn-id: svn://svn.chromium.org/blink/trunk@162508 bbb929c8-8fbe-4397-9dbb-9b2b20218538