Add file modes for opening a file write only

runtime/bin/file.cc

 // 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.
 
 #include "bin/file.h"
 
 #include "bin/builtin.h"
 #include "bin/dartutils.h"
 #include "bin/io_buffer.h"
 #include "bin/utils.h"
@@ skipping 41 matching lines @@
     remaining -= bytes_written;  // Reduce the number of remaining bytes.
     current_buffer += bytes_written;  // Move the buffer forward.
   }
   return true;
 }
 
 
 File::FileOpenMode File::DartModeToFileMode(DartFileOpenMode mode) {
   ASSERT(mode == File::kDartRead ||
          mode == File::kDartWrite ||
-         mode == File::kDartAppend);
+         mode == File::kDartAppend ||
+         mode == File::kDartWriteOnly ||
+         mode == File::kDartWriteOnlyAppend);
   if (mode == File::kDartWrite) {
     return File::kWriteTruncate;
   }
   if (mode == File::kDartAppend) {
     return File::kWrite;
   }
+  if (mode == File::kDartWriteOnly) {
+    return File::kWriteOnlyTruncate;
+  }
+  if (mode == File::kDartWriteOnlyAppend) {
+    return File::kWriteOnly;
+  }
   return File::kRead;
 }
 
 
 void FUNCTION_NAME(File_Open)(Dart_NativeArguments args) {
   const char* filename =
       DartUtils::GetStringValue(Dart_GetNativeArgument(args, 0));
   int64_t mode = DartUtils::GetIntegerValue(Dart_GetNativeArgument(args, 1));
   File::DartFileOpenMode dart_file_mode =
       static_cast<File::DartFileOpenMode>(mode);
@@ skipping 1169 matching lines @@
       }
     } else {
       return CObject::FileClosedError();
     }
   }
   return CObject::IllegalArgumentError();
 }
 
 }  // namespace bin
 }  // namespace dart