This adds a bit of boilerplate to some AstVisitors (they now have to
declare their own zone_ member and zone() accessor), but makes it clearer
what DEFINE_AST_VISITOR_SUBCLASS_MEMBERS is for: stack limit checking.

Review URL: https://codereview.chromium.org/1394303008

Cr-Commit-Position: refs/heads/master@{#31287}