Move the AstVisitor stack check from Accept to Visit.

Move the AstVisitor stack check from Accept to Visit.

The stack check has been moved from the Accept function dispatching on
the AST node type, earlier to the Visit function dispatching on the
visitor type.

This allows very simple non-recursive visitors (not taking extra
arguments or returning values) via the convention of calling "Visit"
if one wants the stack check and "Accept" if one does not.  Recursive
calls should all be via "Visit".

Review URL: http://codereview.chromium.org/1567007

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@4320 ce2b1a6d-e550-0410-aec6-3dcde31c8c00