Add FileHandleFileWriter

util/file/file_io.h

Index: util/file/file_io.h
diff --git a/util/file/file_io.h b/util/file/file_io.h
index ef22e2d7637b558f38c492cd36db990d421c2db1..268bfd3b026ca4c000933f62d2ab88c269b26ae6 100644
--- a/util/file/file_io.h
+++ b/util/file/file_io.h
@@ -43,12 +43,17 @@ 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.