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

test/codegen/expect/syncstar_yield_test.js

-dart_library.library('syncstar_yield_test', null, /* Imports */[
-  "dart_runtime/dart",
-  'dart/core',
-  'expect'
-], /* Lazy imports */[
-], function(exports, dart, core, expect) {
-  'use strict';
-  let dartx = dart.dartx;
-  function* foo1() {
-    yield 1;
-  }
-  dart.fn(foo1, core.Iterable$(core.int), []);
-  function* foo2(p) {
-    let t = false;
-    yield null;
-    while (true) {
-      a:
-        for (let i = 0; dart.notNull(i) < dart.notNull(dart.as(p, core.num)); i = dart.notNull(i) + 1) {
-          if (!dart.notNull(t)) {
-            for (let j = 0; dart.notNull(j) < 3; j = dart.notNull(j) + 1) {
-              yield -1;
-              t = true;
-              break a;
-            }
-          }
-          yield i;
-        }
-    }
-  }
-  dart.fn(foo2, core.Iterable$(core.int), [dart.dynamic]);
-  function* foo3(p) {
-    let i = 0;
-    i = dart.notNull(i) + 1;
-    p = dart.notNull(p) + 1;
-    yield dart.notNull(p) + dart.notNull(i);
-  }
-  dart.fn(foo3, core.Iterable$(core.int), [core.int]);
-  function main() {
-    expect.Expect.listEquals([1], foo1()[dartx.toList]());
-    expect.Expect.listEquals([null, -1, 0, 1, 2, 3, 0, 1, 2, 3], foo2(4)[dartx.take](10)[dartx.toList]());
-    let t = foo3(0);
-    let it1 = t[dartx.iterator];
-    let it2 = t[dartx.iterator];
-    it1.moveNext();
-    it2.moveNext();
-    expect.Expect.equals(2, it1.current);
-    expect.Expect.equals(2, it2.current);
-    expect.Expect.isFalse(it1.moveNext());
-    expect.Expect.isFalse(it1.moveNext());
-    expect.Expect.isFalse(it2.moveNext());
-    expect.Expect.isFalse(it2.moveNext());
-  }
-  dart.fn(main);
-  // Exports:
-  exports.foo1 = foo1;
-  exports.foo2 = foo2;
-  exports.foo3 = foo3;
-  exports.main = main;
-});