[dart:io] Don't close stdin with a socket finalizer

runtime/bin/stdio_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 _StdIOUtils {
   @patch
   static Stdin _getStdioInputStream() {
     switch (_getStdioHandleType(0)) {
       case _STDIO_HANDLE_TYPE_TERMINAL:
       case _STDIO_HANDLE_TYPE_PIPE:
       case _STDIO_HANDLE_TYPE_SOCKET:
         return new Stdin._(new _Socket._readPipe(0));
       case _STDIO_HANDLE_TYPE_FILE:
         return new Stdin._(new _FileStream.forStdin());
       default:
-        throw new FileSystemException("Unsupported stdin type");
+        throw new FileSystemException(
+            "Couldn't determine file type of stdin (fd 0)");
     }
   }
 
   @patch
   static _getStdioOutputStream(int fd) {
     assert(fd == 1 || fd == 2);
     switch (_getStdioHandleType(fd)) {
       case _STDIO_HANDLE_TYPE_TERMINAL:
       case _STDIO_HANDLE_TYPE_PIPE:
       case _STDIO_HANDLE_TYPE_SOCKET:
       case _STDIO_HANDLE_TYPE_FILE:
         return new Stdout._(new IOSink(new _StdConsumer(fd)), fd);
       default:
-        throw new FileSystemException("Unsupported stdin type");
+        throw new FileSystemException(
+            "Couldn't determine file type of stdio handle (fd $fd)");
     }
   }
 
   @patch
   static int _socketType(Socket socket) {
     if (socket is _Socket) return _nativeSocketType(socket._nativeSocket);
     return null;
   }
 
   static int _nativeSocketType(_NativeSocket nativeSocket) {
@@ skipping 102 matching lines @@
       throw new StdoutException("Error determining ANSI support", result);
     }
     return result;
   }
 
   static _getAnsiSupported(int fd) native "Stdout_AnsiSupported";
 }
 
 _getStdioHandle(_NativeSocket socket, int num) native "Socket_GetStdioHandle";
 _getSocketType(_NativeSocket nativeSocket) native "Socket_GetType";