for clarity and consistency with GlobalObject::native_context.

R=svenpanne@chromium.org
BUG=
TEST=

Review URL: https://chromiumcodereview.appspot.com/10861007

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12341 ce2b1a6d-e550-0410-aec6-3dcde31c8c00