Switch from interfaces to abstract classes in dart:io.

runtime/bin/socket.dart

Index: runtime/bin/socket.dart
diff --git a/runtime/bin/socket.dart b/runtime/bin/socket.dart
index 86d5e5f26537728db7f4d8e91c31dae78be5b424..83b16b288cfef5098f27d5c2967a7ce46d87c089 100644
--- a/runtime/bin/socket.dart
+++ b/runtime/bin/socket.dart
@@ -2,12 +2,14 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-interface ServerSocket default _ServerSocket {
+abstract class ServerSocket {
   /**
    * Constructs a new server socket, binds it to a given address and port,
    * and listens on it.
    */
-  ServerSocket(String bindAddress, int port, int backlog);
+  factory ServerSocket(String bindAddress, int port, int backlog) {
+    return new _ServerSocket(bindAddress, port, backlog);
+  }
 
   /**
    * The connection handler gets called when there is a new incoming
@@ -32,13 +34,13 @@ interface ServerSocket default _ServerSocket {
 }
 
 
-interface Socket extends Hashable default _Socket {
+abstract class Socket implements Hashable {
   /**
    * Constructs a new socket and initiate connecting it to the given
    * host on the given port. The returned socket is not yet connected
    * but ready for registration of callbacks.
    */
-  Socket(String host, int port);
+  factory Socket(String host, int port) => new _Socket(host, port);
 
   /**
    * Returns the number of received and non-read bytes in the socket that
@@ -125,7 +127,7 @@ interface Socket extends Hashable default _Socket {
    * possible to read data. Calling [close] will not trigger a call to
    * [onClosed].
    */
-  void close([bool halfClose]);
+  void close([bool halfClose = false]);
 
   /**
    * Socket is hashable.