Call release() when a RefPtr is returned.
https://bugs.webkit.org/show_bug.cgi?id=112420

Patch by Jaehun Lim <ljaehun.lim@samsung.com> on 2013-03-15
Reviewed by Eric Seidel.

release() should be called on a RefPtr to convert it to a PassRefPtr.

No new tests needed, no behavior changes.

* css/CSSParser.cpp:
(WebCore::CSSParser::parseImageResolution):
(WebCore::CSSParser::parseImageSet):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@145892 268f45cc-cd09-0410-ab3c-d52691b4dbfc