Don't clobber SocketError's OSError on failed write and send.

runtime/bin/socket_patch.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // 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.
 
 @patch class RawServerSocket {
   @patch static Future<RawServerSocket> bind(address,
                                                   int port,
                                                   {int backlog: 0,
                                                    bool v6Only: false,
                                                    bool shared: false}) {
@@ skipping 651 matching lines @@
     if (offset is! int || bytes is! int) {
       throw new ArgumentError("Invalid arguments to write on Socket");
     }
     if (isClosing || isClosed) return 0;
     if (bytes == 0) return 0;
     _BufferAndStart bufferAndStart =
         _ensureFastAndSerializableByteData(buffer, offset, offset + bytes);
     var result =
         nativeWrite(bufferAndStart.buffer, bufferAndStart.start, bytes);
     if (result is OSError) {
-      scheduleMicrotask(() => reportError(result, "Write failed"));
+      OSError osError = result;
+      scheduleMicrotask(() => reportError(osError, "Write failed"));
       result = 0;
     }
     // The result may be negative, if we forced a short write for testing
     // purpose. In such case, don't mark writeAvailable as false, as we don't
     // know if we'll receive an event. It's better to just retry.
     if (result >= 0 && result < bytes) {
       writeAvailable = false;
     }
     // Negate the result, as stated above.
     if (result < 0) result = -result;
     // TODO(ricow): Remove when we track internal and pipe uses.
     assert(resourceInfo != null || isPipe || isInternal);
     if (resourceInfo != null) {
       resourceInfo.addWrite(result);
     }
     return result;
   }
 
   int send(List<int> buffer, int offset, int bytes,
            InternetAddress address, int port) {
     _throwOnBadPort(port);
     if (isClosing || isClosed) return 0;
     _BufferAndStart bufferAndStart =
         _ensureFastAndSerializableByteData(
             buffer, offset, bytes);
     var result = nativeSendTo(
         bufferAndStart.buffer, bufferAndStart.start, bytes,
         address._in_addr, port);
     if (result is OSError) {
-      scheduleMicrotask(() => reportError(result, "Send failed"));
+      OSError osError = result;
+      scheduleMicrotask(() => reportError(osError, "Send failed"));
       result = 0;
     }
     // TODO(ricow): Remove when we track internal and pipe uses.
     assert(resourceInfo != null || isPipe || isInternal);
     if (resourceInfo != null) {
       resourceInfo.addWrite(result);
     }
     return result;
   }
 
@@ skipping 1164 matching lines @@
 Datagram _makeDatagram(List<int> data,
                        String address,
                        List<int> in_addr,
                        int port) {
   return new Datagram(
       data,
       new _InternetAddress(address, null, in_addr),
       port);
 }