Keep track of when a socket has been destroyed

sdk/lib/io/http.dart

Index: sdk/lib/io/http.dart
diff --git a/sdk/lib/io/http.dart b/sdk/lib/io/http.dart
index 452dbe7cc4cfa1cc44e50af59b61776d390b4c58..5d316eb7890c5356330b7c30a41fb894f6e9cf5e 100644
--- a/sdk/lib/io/http.dart
+++ b/sdk/lib/io/http.dart
@@ -168,10 +168,13 @@ abstract class HttpServer implements Stream<HttpRequest> {
       => new _HttpServer.listenOn(serverSocket);
 
   /**
-   * Permanently stops this [HttpServer] from listening for new connections.
-   * This closes this [Stream] of [HttpRequest]s with a done event.
+   * Permanently stops this [HttpServer] from listening for new
+   * connections.  This closes this [Stream] of [HttpRequest]s with a
+   * done event. The returned future completes when the server is
+   * stopped. For a server started using [bind] or [bindSecure] this
+   * means that the port listened on no longer in use.
    */
-  void close();
+  Future close();
 
   /**
    * Returns the port that the server is listening on. This can be