TF: Clear upper bits of ConvertFloat64ToUint32 because Win64.

R=bmeurer@chromium.org
BUG=

Review URL: https://codereview.chromium.org/436623002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@22765 ce2b1a6d-e550-0410-aec6-3dcde31c8c00