Add a done getter to Client, Server, and Peer.

lib/src/client.dart

Index: lib/src/client.dart
diff --git a/lib/src/client.dart b/lib/src/client.dart
index f3c63ca97d34e71e8c9f6f1bd3796b8c298795a4..f63fde6cb8ca4d60d2299dcdb0bb0624d191f048 100644
--- a/lib/src/client.dart
+++ b/lib/src/client.dart
@@ -32,6 +32,11 @@ class Client {
   /// completed with those requests' responses.
   final _pendingRequests = new Map<int, Completer>();
 
+  /// Returns a [Future] that completes when the connection is closed.
+  ///
+  /// This is the same future that's returned by [listen].
+  Future get done => _streams.done;
+
   /// Creates a [Client] that writes requests to [requests] and reads responses
   /// from [responses].
   ///