Add point to Window class and Window polyfills of screen.

Add point to Window class and Window polyfills of screen.

BUG=
R=blois@google.com

Committed: https://code.google.com/p/dart/source/detail?r=24987

[Emily Fortuna, 2013-07-13 00:08:07]

This is for https://code.google.com/p/dart/issues/detail?id=11675
I went through the suggested methods, but the Point object somehow indicates
that the x and y values are connected in some fashion, whereas in the scroll
cases scrolling up and down vs side to side did not seem related enough to
express that combination as a point. So ultimately I changed moveTo to accept a
point, and consolidated screenX/screenLeft screenY/screenTop in the process (top
works everywhere but FF, Y works everywhere but IE)

[blois, 2013-07-13 00:27:24]

https://codereview.chromium.org/18920008/diff/1/sdk/lib/html/dart2js/html_dar...
File sdk/lib/html/dart2js/html_dart2js.dart (right):

https://codereview.chromium.org/18920008/diff/1/sdk/lib/html/dart2js/html_dar...
sdk/lib/html/dart2js/html_dart2js.dart:24562: int get screenX() => Device.isIE ?
$dom_screenLeft : $dom_screenX;
no parens

https://codereview.chromium.org/18920008/diff/1/sdk/lib/html/dart2js/html_dar...
sdk/lib/html/dart2js/html_dart2js.dart:24562: int get screenX() => Device.isIE ?
$dom_screenLeft : $dom_screenX;
screenX is supported on IE9, is it buggy?

It's not quite clear from: http://help.dottoro.com/ljtefiui.php

[Emily Fortuna, 2013-07-13 00:32:00]

removed removal of screenTop/Left.

[blois, 2013-07-13 00:36:05]

lgtm

https://codereview.chromium.org/18920008/diff/4001/tools/dom/templates/html/i...
File tools/dom/templates/html/impl/impl_Window.darttemplate (right):

https://codereview.chromium.org/18920008/diff/4001/tools/dom/templates/html/i...
tools/dom/templates/html/impl/impl_Window.darttemplate:281: void moveTo(Point p)
=> $dom_moveTo(p.x, p.y);
I think this is actually an analyzer warning as it implies returning the result
of moveTo (null).

Should be:
void moveTo(Point p) {
  $dom_moveTo(p.x, p.y);
}

[Emily Fortuna, 2013-07-13 00:40:33]

Committed patchset #3 manually as r24987 (presubmit successful).