Revert "Don't zone-register async callbacks for every await call in the VM."

runtime/lib/async_patch.dart

Index: runtime/lib/async_patch.dart
diff --git a/runtime/lib/async_patch.dart b/runtime/lib/async_patch.dart
index d78534719656c37ca06fc3cdc7354a930bbeadad..682ee8b10a4ec2d6b8496a5f06496f428819a00e 100644
--- a/runtime/lib/async_patch.dart
+++ b/runtime/lib/async_patch.dart
@@ -4,181 +4,3 @@
 
 import "dart:_internal";
 
-// We need to pass the value as first argument and leave the second and third
-// arguments empty (used for error handling).
-// See vm/ast_transformer.cc for usage.
-Function _asyncThenWrapperHelper(continuation) {
-  // Any function that is used as an asynchronous callback must be registered
-  // in the current Zone. Normally, this is done by the future when a
-  // callback is registered (for example with `.then` or `.catchError`). In our
-  // case we want to reuse the same callback multiple times and therefore avoid
-  // the multiple registrations. For our internal futures (`_Future`) we can
-  // use the shortcut-version of `.then`, and skip the registration. However,
-  // that means that the continuation must be registered by us.
-  //
-  // Furthermore, we know that the root-zone doesn't actually do anything and
-  // we can therefore skip the registration call for it.
-  //
-  // Note, that the continuation accepts up to three arguments. If the current
-  // zone is the root zone, we don't wrap the continuation, and a bad
-  // `Future` implementation could potentially invoke the callback with the
-  // wrong number of arguments.
-  if (Zone.current == Zone.ROOT) return continuation;
-  return Zone.current.registerUnaryCallback((x) => continuation(x, null, null));
-}
-
-// We need to pass the exception and stack trace objects as second and third
-// parameter to the continuation.  See vm/ast_transformer.cc for usage.
-Function _asyncErrorWrapperHelper(continuation) {
-  // See comments of `_asyncThenWrapperHelper`.
-  var errorCallback = (e, s) => continuation(null, e, s);
-  if (Zone.current == Zone.ROOT) return errorCallback;
-  return Zone.current.registerBinaryCallback(errorCallback);
-}
-
-/// Registers the [thenCallback] and [errorCallback] on the given [object].
-///
-/// If [object] is not a future, then it is wrapped into one.
-///
-/// Returns the result of registering with `.then`.
-Future _awaitHelper(
-    var object, Function thenCallback, Function errorCallback) {
-  if (object is! Future) {
-    object = new _Future().._setValue(object);
-  } else if (object is! _Future) {
-    return object.then(thenCallback, onError: errorCallback);
-  }
-  // `object` is a `_Future`.
-  //
-  // Since the callbacks have been registered in the current zone (see
-  // [_asyncThenWrapperHelper] and [_asyncErrorWrapperHelper]), we can avoid
-  // another registration and directly invoke the no-zone-registration `.then`.
-  //
-  // We can only do this for our internal futures (the default implementation of
-  // all futures that are constructed by the `dart:async` library).
-  return object._thenNoZoneRegistration(thenCallback, errorCallback);
-}
-
-// _AsyncStarStreamController is used by the compiler to implement
-// async* generator functions.
-class _AsyncStarStreamController {
-  StreamController controller;
-  Function asyncStarBody;
-  bool isAdding = false;
-  bool onListenReceived = false;
-  bool isScheduled = false;
-  bool isSuspendedAtYield = false;
-  Completer cancellationCompleter = null;
-
-  Stream get stream => controller.stream;
-
-  void runBody() {
-    isScheduled = false;
-    isSuspendedAtYield = false;
-    asyncStarBody();
-  }
-
-  void scheduleGenerator() {
-    if (isScheduled || controller.isPaused || isAdding) {
-      return;
-    }
-    isScheduled = true;
-    scheduleMicrotask(runBody);
-  }
-
-  // Adds element to steam, returns true if the caller should terminate
-  // execution of the generator.
-  //
-  // TODO(hausner): Per spec, the generator should be suspended before
-  // exiting when the stream is closed. We could add a getter like this:
-  // get isCancelled => controller.hasListener;
-  // The generator would translate a 'yield e' statement to
-  // controller.add(e);
-  // suspend;
-  // if (controller.isCancelled) return;
-  bool add(event) {
-    if (!onListenReceived) _fatal("yield before stream is listened to!");
-    if (isSuspendedAtYield) _fatal("unexpected yield");
-    // If stream is cancelled, tell caller to exit the async generator.
-    if (!controller.hasListener) {
-      return true;
-    }
-    controller.add(event);
-    scheduleGenerator();
-    isSuspendedAtYield = true;
-    return false;
-  }
-
-  // Adds the elements of stream into this controller's stream.
-  // The generator will be scheduled again when all of the
-  // elements of the added stream have been consumed.
-  // Returns true if the caller should terminate
-  // execution of the generator.
-  bool addStream(Stream stream) {
-    if (!onListenReceived) _fatal("yield before stream is listened to!");
-    // If stream is cancelled, tell caller to exit the async generator.
-    if (!controller.hasListener) return true;
-    isAdding = true;
-    var whenDoneAdding =
-        controller.addStream(stream as Stream, cancelOnError: false);
-    whenDoneAdding.then((_) {
-      isAdding = false;
-      scheduleGenerator();
-    });
-    return false;
-  }
-
-  void addError(error, stackTrace) {
-    if ((cancellationCompleter != null) && !cancellationCompleter.isCompleted) {
-      // If the stream has been cancelled, complete the cancellation future
-      // with the error.
-      cancellationCompleter.completeError(error, stackTrace);
-      return;
-    }
-    // If stream is cancelled, tell caller to exit the async generator.
-    if (!controller.hasListener) return;
-    controller.addError(error, stackTrace);
-    // No need to schedule the generator body here. This code is only
-    // called from the catch clause of the implicit try-catch-finally
-    // around the generator body. That is, we are on the error path out
-    // of the generator and do not need to run the generator again.
-  }
-
-  close() {
-    if ((cancellationCompleter != null) && !cancellationCompleter.isCompleted) {
-      // If the stream has been cancelled, complete the cancellation future
-      // with the error.
-      cancellationCompleter.complete();
-    }
-    controller.close();
-  }
-
-  _AsyncStarStreamController(this.asyncStarBody) {
-    controller = new StreamController(onListen: this.onListen,
-                                      onResume: this.onResume,
-                                      onCancel: this.onCancel);
-  }
-
-  onListen() {
-    assert(!onListenReceived);
-    onListenReceived = true;
-    scheduleGenerator();
-  }
-
-  onResume() {
-    if (isSuspendedAtYield) {
-      scheduleGenerator();
-    }
-  }
-
-  onCancel() {
-    if (controller.isClosed) {
-      return null;
-    }
-    if (cancellationCompleter == null) {
-      cancellationCompleter = new Completer();
-      scheduleGenerator();
-    }
-    return cancellationCompleter.future;
-  }
-}