Chromium: Fix scrollbar tickmark drawing on Mountain Lion

Chromium: Fix scrollbar tickmark drawing on Mountain Lion
https://bugs.webkit.org/show_bug.cgi?id=83844

Patch by Sailesh Agrawal <sail@chromium.org> on 2012-04-12
Reviewed by James Robinson.

On Mountain Lion overlay scrollbars have a new expanded mode. In expanded mode the scrolllbar is slightly wider which causes the tickmarks to look incorrect. Fix was to explicitly enter expanded mode to get the correct look.
Screenshots:
broken: http://i.imgur.com/PDKYH.png
fixed: http://i.imgur.com/utp0Y.png

* platform/chromium/ScrollbarThemeChromiumMac.mm:
(WebCore::ScrollbarThemeChromiumMac::paint): Called setExpanded if API is available.
* platform/mac/NSScrollerImpDetails.h: Exposed the isExpanded: API.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@114088 268f45cc-cd09-0410-ab3c-d52691b4dbfc