Revert 172524 "Revert 172495 "Make window.screen property non re..."

The Maps test has been updated as described in the bug, so reverting
my earlier revert to re-land the original CL.

> Revert 172495 "Make window.screen property non replaceable"
> 
> This broke the Maps pixel test on the GPU bots, because it is setting
> window.screen to null to work around a bug in the (somewhat old) version of
> the Maps team's code. We will work with the Maps team to get an updated
> version of the test ASAP, but in the meantime to prevent these bots from
> being red for a day or more I am reverting this change. Sorry.
> 
> http://build.chromium.org/p/chromium.webkit/builders/GPU%20Mac10.7%20%28dbg%29/builds/24997
> 
> > 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
> > 
> > Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=172134
> > 
> > Review URL: https://codereview.chromium.org/243173004
> 
> TBR=ch.dumez@samsung.com
> 
> Review URL: https://codereview.chromium.org/259523005

TBR=kbr@chromium.org

Review URL: https://codereview.chromium.org/276023003

git-svn-id: svn://svn.chromium.org/blink/trunk@173786 bbb929c8-8fbe-4397-9dbb-9b2b20218538