Add HttpServer.idleTimeout for closing idle keep-alive connections.

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 1433ac8244a4b0ee84bd0e0fcdbb537c147c6373..df228f522c69b53bdb34c446c687911e1021c30b 100644
--- a/sdk/lib/io/http.dart
+++ b/sdk/lib/io/http.dart
@@ -204,6 +204,17 @@ abstract class HttpServer implements Stream<HttpRequest> {
    * added to each response.
    */
   String serverHeader;
+
+  /**
+   * Get or set the timeout used for idle keep-alive connections. If no further
+   * request is seen within [idleTimeout] after the previous request was
+   * completed, the connection is droped.
+   *
+   * Default is 120 seconds.
+   *
+   * To disable, set [idleTimeout] to `null`.
+   */
+  Duration idleTimeout;
 }