Update documentation for "close".

sdk/lib/async/stream_controller.dart

Index: sdk/lib/async/stream_controller.dart
diff --git a/sdk/lib/async/stream_controller.dart b/sdk/lib/async/stream_controller.dart
index 34582ae7a27603b74dcc2e17ccb64f2c1017593b..547ba9a266ea495ef2ebe093dc54f34d4f7d90b2 100644
--- a/sdk/lib/async/stream_controller.dart
+++ b/sdk/lib/async/stream_controller.dart
@@ -408,15 +408,17 @@ abstract class _StreamController<T> implements StreamController<T>,
   }
 
   /**
-   * Closes this controller.
+   * Closes this controller and sends a done event on the stream.
    *
    * After closing, no further events may be added using [add] or [addError].
    *
    * You are allowed to close the controller more than once, but only the first
    * call has any effect.
    *
-   * The first time a controller is closed, a "done" event is sent to its
+   * The first time a controller is closed, a "done" event is added to its
    * stream.
+   *
+   * The returned future is completed when the done event has been delivered.
    */
   Future close() {
     if (isClosed) {