Little optimization for CSSParser::parseFillShorthand.

Little optimization for CSSParser::parseFillShorthand.
https://bugs.webkit.org/show_bug.cgi?id=79042

Reviewed by Hajime Morita.

Remove one extra loop that we can combine with the following one
which adds the properties to the parser's list of properties. I also
removed a useless check.
Instruments shows on the css-parser-yui benchmark an improvement
of 13ms (from 77ms spent in the function to 64ms).

No new tests : refactoring, existings tests should cover.

* css/CSSParser.cpp:
(WebCore::CSSParser::parseFillShorthand):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@108365 268f45cc-cd09-0410-ab3c-d52691b4dbfc