visibility=[hidden|default], that controls visibility and make
'hidden' the default.  Export a few variables that had been forgotten.

Review URL: http://codereview.chromium.org/206011


git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@2884 ce2b1a6d-e550-0410-aec6-3dcde31c8c00