Do *not* make file handles inheritable on Windows.

runtime/bin/file_win.cc

 // Copyright (c) 2012, 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.
 
 #include "bin/file.h"
 
 #include <fcntl.h>
 #include <io.h>
 #include <stdio.h>
 #include <string.h>
@@ skipping 79 matching lines @@
   ASSERT(handle_->fd() >= 0);
   struct stat st;
   if (fstat(handle_->fd(), &st) == 0) {
     return st.st_size;
   }
   return -1;
 }
 
 
 File* File::Open(const char* name, FileOpenMode mode) {
-  int flags = O_RDONLY | O_BINARY;
+  int flags = O_RDONLY | O_BINARY | O_NOINHERIT;
   if ((mode & kWrite) != 0) {
-    flags = (O_RDWR | O_CREAT | O_BINARY);
+    flags = (O_RDWR | O_CREAT | O_BINARY | O_NOINHERIT);
   }
   if ((mode & kTruncate) != 0) {
     flags = flags | O_TRUNC;
   }
   int fd = open(name, flags, 0666);
   if (fd < 0) {
     return NULL;
   }
   if (((mode & kWrite) != 0) && ((mode & kTruncate) == 0)) {
     int position = lseek(fd, 0, SEEK_END);
@@ skipping 112 matching lines @@
 const char* File::StringEscapedPathSeparator() {
   return "\\\\";
 }
 
 
 File::StdioHandleType File::GetStdioHandleType(int fd) {
   // Treat all stdio handles as pipes. The Windows event handler and
   // socket code will handle the different handle types.
   return kPipe;
 }