fixes #221, initial sync*, async, async* implementation

test/codegen/expect/syncstar_yieldstar_test.js

-dart_library.library('syncstar_yieldstar_test', null, /* Imports */[
-  "dart_runtime/dart",
-  'dart/core',
-  'expect'
-], /* Lazy imports */[
-], function(exports, dart, core, expect) {
-  'use strict';
-  let dartx = dart.dartx;
-  function* bar() {
-    let i = 1;
-    let j = 1;
-    while (true) {
-      yield i;
-      j = dart.notNull(i) + dart.notNull(j);
-      i = dart.notNull(j) - dart.notNull(i);
-    }
-  }
-  dart.fn(bar);
-  function* foo() {
-    yield* [1, 2, 3];
-    yield null;
-    yield* dart.as(bar(), core.Iterable);
-  }
-  dart.fn(foo);
-  function main() {
-    expect.Expect.listEquals([1, 2, 3, null, 1, 1, 2, 3, 5], dart.as(dart.dsend(dart.dsend(foo(), 'take', 9), 'toList'), core.List));
-  }
-  dart.fn(main);
-  // Exports:
-  exports.bar = bar;
-  exports.foo = foo;
-  exports.main = main;
-});