Revert 236048 "Rename RootWindowHost* to WindowTreeHost*"

> Rename RootWindowHost* to WindowTreeHost*
> 
> TBR=sky@chromium.org
> http://crbug.com/308843
> 
> Review URL: https://codereview.chromium.org/76583003

TBR=ben@chromium.org

Review URL: https://codereview.chromium.org/77203002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@236093 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 236093