win: Add open equivalent

util/file/string_file_writer.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 29 matching lines @@
   //! \brief Returns a string containing the virtual file’s contents.
   const std::string& string() const { return string_; }
 
   //! \brief Resets the virtual file’s contents to be empty, and resets its file
   //!     position to `0`.
   void Reset();
 
   // FileWriterInterface:
   bool Write(const void* data, size_t size) override;
   bool WriteIoVec(std::vector<WritableIoVec>* iovecs) override;
-  off_t Seek(off_t offset, int whence) override;
+  FileOffset Seek(FileOffset offset, int whence) override;
 
  private:
   //! \brief The virtual file’s contents.
   std::string string_;
 
   //! \brief The file offset of the virtual file.
   //!
   //! \note This is stored in a `size_t` to match the characteristics of
   //!     #string_, the `std::string` used to store the virtual file’s contents.
   //!     This type will have different characteristics than the `off_t` used to
   //!     report file offsets. The implementation must take care when converting
   //!     between these distinct types.
   base::CheckedNumeric<size_t> offset_;
 
   DISALLOW_COPY_AND_ASSIGN(StringFileWriter);
 };
 
 }  // namespace crashpad
 
 #endif  // CRASHPAD_UTIL_FILE_STRING_FILE_WRITER_H_