Add ability to send a ping interval on a WebSocket.

sdk/lib/io/websocket.dart

Index: sdk/lib/io/websocket.dart
diff --git a/sdk/lib/io/websocket.dart b/sdk/lib/io/websocket.dart
index 370d694f0b04de4d0a50b0a89cb9f5241298d8d0..c30bdc83bb5f1da7fc99ab9a711546a5a6b65990 100644
--- a/sdk/lib/io/websocket.dart
+++ b/sdk/lib/io/websocket.dart
@@ -131,6 +131,18 @@ abstract class WebSocket implements Stream, StreamSink {
   String get closeReason;
 
   /**
+   * Set and get the interval for sending ping signals. If a ping message is not
+   * answered, the `WebSocket` is assumed disconnected and the connection is

[Søren Gjesse, 2013/07/24 11:12:45]

add "by a pong message from the peer" after answered

[Anders Johnsen, 2013/07/24 12:14:23]

Done.

+   * closed. When a ping signal is sent, the pong message must be received

[Søren Gjesse, 2013/07/24 11:12:45]

Add information on the close status used.

[Anders Johnsen, 2013/07/24 12:14:23]

Done.

+   * within [pingInterval].
+   *
+   * Set the [pingInterval] to `null` to disable sending ping messages.
+   *
+   * The default value is `null`.
+   */
+  Duration pingInterval;
+
+  /**
    * Closes the web socket connection. Set the optional [code] and [reason]
    * arguments to send close information to the remote peer. If they are
    * omitted, the peer will see [WebSocketStatus.NO_STATUS_RECEIVED] code