[BlackBerry] add a way to overscroll non-overflown content

https://bugs.webkit.org/show_bug.cgi?id=96331
PR #195305

Patch by Antonio Gomes <agomes@rim.com> on 2012-09-11
Reviewed by Yong Li.

Check -webkit-overflow-scrolling value for '-blackberry-touch' instead
of checking a custom HTML5 attribute.

No behavioural change. Mostly a rework of r128142.

* Api/InRegionScroller.cpp:
(BlackBerry::WebKit::canScrollRenderBox):

git-svn-id: svn://svn.chromium.org/blink/trunk@128230 bbb929c8-8fbe-4397-9dbb-9b2b20218538