Unreviewed build fix after r159526.
isBoxValue is used at out of ENABLE_CSS_SHAPES gaurd. It causes a compile failure.
So I moved isBoxValue to out side of ENABLE_CSS_SHAPES.

* css/CSSParser.cpp:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@161086 268f45cc-cd09-0410-ab3c-d52691b4dbfc