Make window.screen property non replaceable

Make window.screen property non replaceable for consistency with other
browsers (tested with Firefox 28 and IE11).

This CL also adds an internals.setOverrideScreenData() utility function for
Layout tests as the fast/forms/page-popup/page-popup-adjust-rect.html test
needs to be able to override the screen object.

BUG=364937
TEST=fast/dom/Window/get-set-properties.html

Review URL: https://codereview.chromium.org/243173004

git-svn-id: svn://svn.chromium.org/blink/trunk@172134 bbb929c8-8fbe-4397-9dbb-9b2b20218538