Fix HTTP sample implementation to actually wait for connections before attempting to write.

samples/chat/http.dart

Index: samples/chat/http.dart
diff --git a/samples/chat/http.dart b/samples/chat/http.dart
index 9f1c6f952c1445e765a0e7b76d638c1cf4410c7b..19118a9810a63b20ad764c984b498b89e9bc8a4a 100644
--- a/samples/chat/http.dart
+++ b/samples/chat/http.dart
@@ -203,14 +203,21 @@ interface HTTPClient factory HTTPClientImplementation {
   HTTPClient();
 
   /**
-   * Open a HTTP connection.
+   * Open a HTTP connection. The [openHandler] is called with an
+   * HTTPClientRequest when the connection has been successfully
+   * opened.
    */
-  HTTPClientRequest open(String method, String host, int port, String path);
+  void open(String method, String host, int port, String path);
 
   /**
    * Shutdown the HTTP client releasing all resources.
    */
   void shutdown();
+
+  /**
+   * Set the open handler that is called on successful open operations.
+   */
+  void set openHandler(void handler(HTTPClientRequest request));
 }