Fix Stream.distinct.

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 64a525f1f30dcd6d7ae258c35bc761661c8f4ab5..9c83e1966b0b45694808dc2dc7423e113a458c75 100644
--- a/sdk/lib/async/stream.dart
+++ b/sdk/lib/async/stream.dart
@@ -1022,10 +1022,17 @@ abstract class Stream<T> {
    *
    * The returned stream provides the same events as this stream, except
    * that it never provides two consecutive data events that are equal.
+   * That is, errors are passed through to the returned stream, and
+   * data events are passed through if they are distinct from the most
+   * recently emitted data event.
    *
    * Equality is determined by the provided [equals] method. If that is
    * omitted, the '==' operator on the last provided data element is used.
    *
+   * If [equals] throws, the data event is replaced by an error event
+   * containing the thrown error. The behavior is equivalent to the
+   * original stream emitting the error event.
+   *
    * The returned stream is a broadcast stream if this stream is.
    * If a broadcast stream is listened to more than once, each subscription
    * will individually perform the `equals` test.