Implementation of async-await transformation on js ast.

tests/language/asyncstar_yieldstar_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.
+
+import "dart:async";
+import "package:expect/expect.dart";
+import "package:async_helper/async_helper.dart";
+
+Stream<int> subStream(p) async* {
+  yield p;
+  yield p+1;
+}
+
+Stream foo(Completer<bool> finalized) async* {
+  int i = 0;
+  try {
+    while (true) {
+      yield "outer";
+      yield* subStream(i);
+      i++;
+    }
+  } finally {
+    // See that we did not run too many iterations.
+    Expect.isTrue(i < 10);
+    // Canceling the stream-subscription should run the finalizer.
+    finalized.complete(true);
+  }
+}
+
+foo2(Stream subStream) async* {
+  yield* subStream;
+}
+
+main () async {
+  asyncStart();
+  print("starting");
+  Expect.listEquals([0, 1],
+      await (subStream(0).toList()));
+  Completer<bool> finalized = new Completer<bool>();
+  Expect.listEquals(["outer", 0, 1, "outer", 1, 2, "outer", 2],
+      await (foo(finalized).take(8).toList()));
+  Expect.isTrue(await (finalized.future));
+  
+  finalized = new Completer<bool>();
+  // Canceling the stream while it is yield*-ing from the sub-stream.
+  Expect.listEquals(["outer", 0, 1, "outer", 1, 2, "outer"],
+      await (foo(finalized).take(7).toList()));
+  Expect.isTrue(await (finalized.future));
+  finalized = new Completer<bool>();
+ 
+  Completer<bool> pausedCompleter = new Completer<bool>();
+  Completer<bool> resumedCompleter = new Completer<bool>();
+ 
+  StreamController controller;
+  int i = 0;
+  addNext() {
+    if (i >= 4) return;
+    controller.add(i);
+    i++;
+    if (!controller.isPaused) {
+      scheduleMicrotask(addNext);
+    }
+  }
+ 
+  controller = new StreamController(onListen: () {
+    scheduleMicrotask(addNext);
+  }, onPause: () {
+    pausedCompleter.complete(true);
+  }, onResume: () {
+    resumedCompleter.complete(true);
+    scheduleMicrotask(addNext);
+  });
+ 
+  StreamSubscription subscription;
+  // Test that the yield*'ed stream is paused and resumed.
+  subscription = foo2(controller.stream).listen((event) {
+    if (event == 2) {
+      subscription.pause();
+      scheduleMicrotask(() {
+        subscription.resume();
+      });
+    }
+  });
+  Expect.isTrue(await (pausedCompleter.future));
+  Expect.isTrue(await (resumedCompleter.future));
+  asyncEnd();
+}