Statically type check "generic" methods

[vsmenon]

We need to be able to statically type check methods such as Iterable.map. E.g., this should not trigger a warning:

Iterable<int> incr(Iterable<int> iter) => iter.map((int x) => x + 1);

Initially, we can annotate / whitelist methods that should be treated as generic.

See #28 for general bug on generic methods.

[vsmenon]

Note, the code in the first comment is now handled by our initial whitelist implementation, but we're not doing any inference yet. The following variant (with less typing on the closure) is still not handled:

Iterable<int> incr(Iterable<int> iter) => iter.map((x) => x + 1);

[alorenzen]

Another example of "generic" methods is Future.then, in which a Future<T>.then((T)->V) should return a Future<V>.

[jmesserly]

Vijay fixed this a while ago (at first with a hard coded list). Support for comment-based annotations is mostly done as well.