implement generic method runtime behavior, fixes #301

test/codegen/expect/closure.js

 export const closure = Object.create(null);
 import { core, js, dart, dartx } from 'dart_sdk';
-closure.generic_function = function<T>(items: core.List<T>, seed: T): core.List<T> {
-  let strings = items[dartx.map](dart.fn((i: T): string => `${i}`, core.String, [dart.dynamic]))[dartx.toList]();
-  return items;
+closure.generic_function = function(T) {
+  return (items: core.List<T>, seed: T): core.List<T> => {
+    let strings = items[dartx.map](core.String)(dart.fn((i: T): string => `${i}`, core.String, [T]))[dartx.toList]();
+    return items;
+  };
 };
-dart.fn(closure.generic_function, core.List, [core.List, dart.dynamic]);
+dart.fn(closure.generic_function, T => [core.List$(T), [core.List$(T), T]]);
 closure.Callback = dart.typedef('Callback', () => dart.functionType(dart.void, [], {i: core.int}));
 closure.Foo$ = dart.generic(T => {
   class Foo<T> extends core.Object {
     i: number;
     b: boolean;
     s: string;
     v: T;
     static some_static_constant: string;
     static some_static_final: string;
     static some_static_var: string;
@@ skipping 72 matching lines @@
 });
 closure.main = function(args): void {
 };
 dart.fn(closure.main, dart.void, [dart.dynamic]);
 /** @final {string} */
 closure.some_top_level_constant = "abc";
 /** @final {string} */
 closure.some_top_level_final = "abc";
 /** @type {string} */
 closure.some_top_level_var = "abc";