Fixed a number of bugs on RawSocket and Socket

sdk/lib/io/socket.dart

Index: sdk/lib/io/socket.dart
diff --git a/sdk/lib/io/socket.dart b/sdk/lib/io/socket.dart
index d703c8de08ddbc6f1487429ce5ff83c7ff66ac89..9152beebda0ea1b0457906ca209e4f44b0b52ade 100644
--- a/sdk/lib/io/socket.dart
+++ b/sdk/lib/io/socket.dart
@@ -763,6 +763,7 @@ class SocketException implements IOException {
   final int port;
 
   const SocketException(this.message, {this.osError, this.address, this.port});
+  const SocketException.closed() : message = 'Socket has been closed';
 
   String toString() {
     StringBuffer sb = new StringBuffer();