Add FileReaderInterface. Move StringFileWriter to StringFile and

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,
-// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-// See the License for the specific language governing permissions and
-// limitations under the License.
-
-#ifndef CRASHPAD_UTIL_FILE_STRING_FILE_WRITER_H_
-#define CRASHPAD_UTIL_FILE_STRING_FILE_WRITER_H_
-
-#include <sys/types.h>
-
-#include <string>
-
-#include "base/basictypes.h"
-#include "base/numerics/safe_math.h"
-#include "util/file/file_writer.h"
-
-namespace crashpad {
-
-//! \brief A file writer backed by a virtual file, as opposed to a file on disk
-//!     or other operating system file descriptor-based file.
-//!
-//! The virtual file is a buffer in memory. This class is convenient for use
-//! with other code that normally expects to write files, when it is impractical
-//! or inconvenient to write a file. It is expected that tests, in particular,
-//! will benefit from using this class.
-class StringFileWriter : public FileWriterInterface {
- public:
-  StringFileWriter();
-  ~StringFileWriter();
-
-  //! \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;
-  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_