Add FileHandleFileWriter

util/file/file_io.h

 // Copyright 2014 The Crashpad Authors. All rights reserved.
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //     http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
@@ skipping 25 matching lines @@
 
 //! \brief Platform-specific alias for a low-level file handle.
 using FileHandle = int;
 
 //! \brief Platform-specific alias for a position in an open file.
 using FileOffset = off_t;
 
 //! \brief Scoped wrapper of a FileHandle.
 using ScopedFileHandle = base::ScopedFD;
 
+//! \brief A value that can never be a valid FileHandle.
+const FileHandle kInvalidFileHandle = -1;
+
 #elif defined(OS_WIN)
 
 using FileHandle = HANDLE;
 using FileOffset = LONGLONG;
 using ScopedFileHandle = ScopedFileHANDLE;
 
+const FileHandle kInvalidFileHandle = INVALID_HANDLE_VALUE;
+
 #endif
 
 //! \brief Determines the mode that LoggingOpenFileForWrite() uses.
 enum class FileWriteMode {
   //! \brief Opens the file if it exists, or creates a new file.
   kReuseOrCreate,
 
   //! \brief Creates a new file. If the file already exists, it will be
   //!     overwritten.
   kTruncateOrCreate,
@@ skipping 146 matching lines @@
 
 //! \brief Wraps `close()` or `CloseHandle()`, ensuring that it succeeds.
 //!
 //! If the underlying function fails, this function causes execution to
 //! terminate without returning.
 void CheckedCloseFile(FileHandle file);
 
 }  // namespace crashpad
 
 #endif  // CRASHPAD_UTIL_FILE_FILE_IO_H_