Add file modes for opening a file write only

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 "platform/globals.h"
 #if defined(TARGET_OS_WINDOWS)
 
 #include "bin/file.h"
 
 #include <fcntl.h>  // NOLINT
@@ skipping 139 matching lines @@
   if (_fstat64(handle_->fd(), &st) == 0) {
     return st.st_size;
   }
   return -1;
 }
 
 
 File* File::Open(const char* name, FileOpenMode mode) {
   int flags = O_RDONLY | O_BINARY | O_NOINHERIT;
   if ((mode & kWrite) != 0) {
+    ASSERT((mode & kWriteOnly) == 0);
     flags = (O_RDWR | O_CREAT | O_BINARY | O_NOINHERIT);
   }
+  if ((mode & kWriteOnly) != 0) {
+    ASSERT((mode & kWrite) == 0);
+    flags = (O_WRONLY | O_CREAT | O_BINARY | O_NOINHERIT);
+  }
   if ((mode & kTruncate) != 0) {
     flags = flags | O_TRUNC;
   }
   const wchar_t* system_name = StringUtils::Utf8ToWide(name);
   int fd = _wopen(system_name, flags, 0666);
   free(const_cast<wchar_t*>(system_name));
   if (fd < 0) {
     return NULL;
   }
-  if (((mode & kWrite) != 0) && ((mode & kTruncate) == 0)) {
+  if ((((mode & kWrite) != 0) && ((mode & kTruncate) == 0)) ||
+      (((mode & kWriteOnly) != 0) && ((mode & kTruncate) == 0))) {
     int64_t position = _lseeki64(fd, 0, SEEK_END);
     if (position < 0) {
       return NULL;
     }
   }
   return new File(new FileHandle(fd));
 }
 
 
 File* File::OpenStdio(int fd) {
@@ skipping 502 matching lines @@
     return kIdentical;
   } else {
     return kDifferent;
   }
 }
 
 }  // namespace bin
 }  // namespace dart
 
 #endif  // defined(TARGET_OS_WINDOWS)