Introduce is_debuggable state bit on function objects

Simplify debugger logic. Any function can be marked as
non-debuggable when is is created. The debugger no longer
needs a heuristic which functions are debuggable.
Mostly used for synthetic, generated functions that
have no source code, e.g. async code, implicit getters and
setters, implicit constructors, forwarding constructors,
dispatcher functions.

Review URL: https://codereview.chromium.org//789643006

git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42570 260f80e4-7a28-3924-810f-c04153c831b5
- Update svn:ignore lists.



git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge@42571 260f80e4-7a28-3924-810f-c04153c831b5