Add FileReaderInterface::ReadExactly() and FileSeekerInterface::SeekSet()

util/file/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 24 matching lines @@
 struct WritableIoVec {
   //! \brief The base address of a memory region for output.
   const void* iov_base;
 
   //! \brief The size of the memory pointed to by #iov_base.
   size_t iov_len;
 };
 
 //! \brief An interface to write to files and other file-like objects with
 //!     semantics matching the underlying platform (POSIX or Windows).
-class FileWriterInterface : public FileSeekerInterface {
+class FileWriterInterface : public virtual FileSeekerInterface {
  public:
   //! \brief Wraps LoggingWriteFile(), or provides an implementation with
   //!     identical semantics.
   //!
   //! \return `true` if the operation succeeded, `false` if it failed, with an
   //!     error message logged.
   virtual bool Write(const void* data, size_t size) = 0;
 
   //! \brief Wraps `writev()` on POSIX or provides an alternate implementation
   //!     with identical semantics. This method will write entire buffers,
@@ skipping 108 matching lines @@
  private:
   ScopedFileHandle file_;
   WeakFileHandleFileWriter weak_file_handle_file_writer_;
 
   DISALLOW_COPY_AND_ASSIGN(FileWriter);
 };
 
 }  // namespace crashpad
 
 #endif  // CRASHPAD_UTIL_FILE_FILE_WRITER_H_