Revert "Add groupBy to Stream."

sdk/lib/async/stream.dart

Index: sdk/lib/async/stream.dart
diff --git a/sdk/lib/async/stream.dart b/sdk/lib/async/stream.dart
index bf7840912d8846ff2cf2b2a7ad3d12d7b3bef68f..5de26b579e0abb372c8f763f59744ee4f783daab 100644
--- a/sdk/lib/async/stream.dart
+++ b/sdk/lib/async/stream.dart
@@ -395,76 +395,6 @@ abstract class Stream<T> {
     return new _MapStream<T, S>(this, convert);
   }
 
-  /// Groups events by a computed key.
-  ///
-  /// A key is extracted from incoming events.
-  /// The first time a key is seen, a stream is created for it, and emitted
-  /// on the returned stream, along with the key, as a [GroupedEvents] object.
-  /// Then the event is emitted on the stream ([GroupedEvents.values])
-  /// corresponding to the key.
-  ///
-  /// An error on the source stream, or when calling the `key` functions,
-  /// will emit the error on the returned stream.
-  ///
-  /// Canceling the subscription on the returned stream will stop processing
-  /// and close the streams for all groups.
-  ///
-  /// Pausing the subscription on the returned stream will pause processing
-  /// and no further events are added to streams for the individual groups.
-  ///
-  /// Pausing or canceling an individual group stream has no effect other than
-  /// on that stream. Events will be queued while the group stream
-  /// is paused and until it is first listened to.
-  /// If the [GroupedEvents.values] stream is never listened to,
-  /// it will enqueue all the events unnecessarily.
-  Stream<GroupedEvents<K, T>> groupBy<K>(K key(T event)) {
-    var controller;
-    controller = new StreamController<GroupedEvents<K, T>>(
-        sync: true,
-        onListen: () {
-          var groupControllers = new HashMap<K, StreamController<T>>();
-
-          void closeAll() {
-            for (var groupController in groupControllers.values) {
-              groupController.close();
-            }
-          }
-
-          var subscription = this.listen(
-              (data) {
-                K theKey;
-                try {
-                  theKey = key(data);
-                } catch (error, stackTrace) {
-                  controller.addError(error, stackTrace);
-                  return;
-                }
-                var groupController = groupControllers[theKey];
-                if (groupController == null) {
-                  groupController =
-                      new StreamController<T>.broadcast(sync: true);
-                  groupControllers[theKey] = groupController;
-                  controller.add(
-                      new GroupedEvents<K, T>(theKey, groupController.stream));
-                }
-                groupController.add(data);
-              },
-              onError: controller.addError,
-              onDone: () {
-                controller.close();
-                closeAll();
-              });
-          controller.onPause = subscription.pause;
-          controller.onResume = subscription.resume;
-          controller.onCancel = () {
-            subscription.cancel();
-            // Don't fire sync events in response to a callback.
-            scheduleMicrotask(closeAll);
-          };
-        });
-    return controller.stream;
-  }
-
   /**
    * Creates a new stream with each data event of this stream asynchronously
    * mapped to a new event.
@@ -2067,36 +1997,3 @@ class _ControllerEventSinkWrapper<T> implements EventSink<T> {
     _sink.close();
   }
 }
-
-/// A group created by [Stream.groupBy].
-///
-/// The stream created by `groupBy` emits a `GroupedEvents`
-/// for each distinct key it encounters.
-/// This group contains the [key] itself, along with a stream of the [values]
-/// associated with that key.
-class GroupedEvents<K, V> {
-  /// The key that identifiers the values emitted by [values].
-  final K key;
-
-  /// The [values] that [GroupBy] have grouped by the common [key].
-  final Stream<V> values;
-
-  factory GroupedEvents(K key, Stream<V> values) = GroupedEvents<K, V>._;
-
-  // Don't expose a generative constructor.
-  // This class is not intended for subclassing, so we don't want to promise
-  // it. We can change that in the future.
-  GroupedEvents._(this.key, this.values);
-
-  /// Tells [values] to discard values instead of retaining them.
-  ///
-  /// Must only be used instead of listening to the [values] stream.
-  /// If the stream has been listened to, this call fails.
-  /// After calling this method, listening on the [values] stream fails.
-  Future cancel() {
-    // If values has been listened to,
-    // this throws a StateError saying that stream has already been listened to,
-    // which is a correct error message for this call too.
-    return values.listen(null).cancel();
-  }
-}