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

util/file/file_seeker.h

 // Copyright 2015 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 12 matching lines @@
 //!     semantics matching the underlying platform (POSIX or Windows).
 class FileSeekerInterface {
  public:
   //! \brief Wraps LoggingFileSeek() or provides an alternate implementation
   //!     with identical semantics.
   //!
   //! \return The return value of LoggingFileSeek(). `-1` on failure,
   //!     with an error message logged.
   virtual FileOffset Seek(FileOffset offset, int whence) = 0;
 
+  //! \brief Wraps Seek(), using `SEEK_CUR` to obtain the file’s current
+  //!     position.
+  //!
+  //! \return The file’s current position on success. `-1` on failure, with an
+  //!     error message logged.
+  FileOffset SeekGet();
+
+  //! \brief Wraps Seek(), using `SEEK_SET`, ensuring that the seek succeeded
+  //!     and the file is positioned as desired.
+  //!
+  //! \return `true` if the operation succeeded, `false` if it failed, with an
+  //!     error message logged. A failure to reposition the file as desired is
+  //!     treated as a failure.
+  bool SeekSet(FileOffset offset);
+
  protected:
   ~FileSeekerInterface() {}
 };
 
 }  // namespace crashpad
 
 #endif  // CRASHPAD_UTIL_FILE_FILE_SEEKER_H_