Warning by some gcc versions. Adding the parenthesis made the condition correct.

TBR=ager@chromium.org
Review URL: http://codereview.chromium.org/2725003

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4821 ce2b1a6d-e550-0410-aec6-3dcde31c8c00