Get rid of custom code for Window.location attribute setter

Get rid of custom code for Window.location attribute setter by leveraging
the generator support for [PutForwards=x] IDL extended attribute.

BUG=307045
R=haraken

Review URL: https://codereview.chromium.org/27400003

git-svn-id: svn://svn.chromium.org/blink/trunk@159737 bbb929c8-8fbe-4397-9dbb-9b2b20218538