Add support for sync* and yield

tests/language/sync_generator2_test.dart

+// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Simple test program for sync* generator functions.
+
+import "package:expect/expect.dart";
+import "dart:async";
+
+var sync = "topLevelSync";
+var async = "topLevelAync";
+var await = "topLevelAwait";
+var yield = "topLevelYield";
+
+test01() sync* {
+  var yield = 0;  /// 01: compile-time error
+  var await = 0;  /// 02: compile-time error
+  var async = 0;  /// 03: compile-time error
+  bool yield() => false; /// 04: compile-time error
+  bool await() => false; /// 05: compile-time error
+  bool async() => false; /// 06: compile-time error
+
+  var x1 = sync;
+  var x2 = async;  /// 07: compile-time error
+  var x3 = await;  /// 08: compile-time error
+  var x4 = await 55;  /// 09: compile-time error
+  var x4 = yield;  /// 10: compile-time error
+
+  var stream = new Stream.fromIterable([1, 2, 3]);
+  await for (var e in stream) print(e);   /// 11: compile-time error
+}
+
+test02() sync* {
+  yield 12321;
+  return null;  /// 20: compile-time error
+}
+
+test03() sync* => null;   /// 30: compile-time error
+
+get test04 sync* => null;  /// 40: compile-time error
+set test04(a) sync* { print(a); }  /// 41: compile-time error
+
+class K {
+  K() sync* {};  /// 50: compile-time error
+  get nix sync* { }
+  get garnix sync* => null;  /// 51: compile-time error
+  set etwas(var z) sync* { }  /// 52: compile-time error
+  sync() sync* {
+    yield sync;  // Yields a tear-off of the sync() method.
+  }
+}
+
+main() {
+  var x;
+  x = test01();
+  Expect.equals("()", x.toString());
+  x = test02();
+  Expect.equals("(12321)", x.toString());
+  x = test04;  /// 40: continued
+  test04 = x;  /// 41: continued
+  x = new K();
+  Expect.equals(1, x.sync().length);
+  Expect.isTrue(x.sync().single is Function);
+}